What And How In Java: Questions

Showing posts with label Questions. Show all posts

Tuesday, 10 April 2012

Interview Questions on Java

Q : What if the main method is declared as private?

The program compiles properly but at runtime it will give “Main method not public.” message.
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Q : What is meant by pass by reference and pass by value in Java?

Pass by reference means, passing the address itself rather than passing the value. Pass by value means passing a copy of the value.
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Q : If you’re overriding the method equals() of an object, which other method you might also consider?

hashCode()
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Q : What is Byte Code?

Or

Q : What gives java it’s “write once and run anywhere” nature?

All Java programs are compiled into class files that contain bytecodes. These byte codes can be run in any platform and hence java is said to be platform independent.
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Q : Expain the reason for each keyword of public static void main(String args[])?

public- main(..) is the first method called by java environment when a program is executed so it has to accessible from java environment. Hence the access specifier has to be public.

static: Java environment should be able to call this method without creating an instance of the class , so this method must be declared as static.

void: main does not return anything so the return type must be void

The argument String indicates the argument type which is given at the command line and arg is an array for string given during command line.
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Q : What are the differences between == and .equals() ?

Or

Q : what is difference between == and equals

Or

Q : Difference between == and equals method

Or

Q : What would you use to compare two String variables – the operator == or the method equals()?

Or

Q : How is it possible for two String objects with identical values not to be equal under the == operator?

The == operator compares two objects to determine if they are the same object in memory i.e. present in the same memory location. It is possible for two String objects to have the same value, but located in different areas of memory.

== compares references while .equals compares contents. The method public boolean equals(Object obj) is provided by the Object class and can be overridden. The default implementation returns true only if the object is compared with itself, which is equivalent to the equality operator == being used to compare aliases to the object. String, BitSet, Date, and File override the equals() method. For two String objects, value equality means that they contain the same character sequence. For the Wrapper classes, value equality means that the primitive values are equal.

public class EqualsTest {

public static void main(String[] args) {

String s1 = "abc";
String s2 = s1;
String s5 = "abc";
String s3 = new String("abc");
String s4 = new String("abc");
System.out.println("== comparison : " + (s1 == s5));
System.out.println("== comparison : " + (s1 == s2));
System.out.println("Using equals method : " + s1.equals(s2));
System.out.println("== comparison : " + s3 == s4);
System.out.println("Using equals method : " + s3.equals(s4));
}
}

Output
== comparison : true
== comparison : true
Using equals method : true
false
Using equals method : true
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Q : What if the static modifier is removed from the signature of the main method?

Or
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Q : What if I do not provide the String array as the argument to the method?

Program compiles. But at runtime throws an error “NoSuchMethodError”.
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Q : Why oracle Type 4 driver is named as oracle thin driver?

Oracle provides a Type 4 JDBC driver, referred to as the Oracle “thin” driver. This driver includes its own implementation of a TCP/IP version of Oracle’s Net8 written entirely in Java, so it is platform independent, can be downloaded to a browser at runtime, and does not require any Oracle software on the client side. This driver requires a TCP/IP listener on the server side, and the client connection string uses the TCP/IP port address, not the TNSNAMES entry for the database name.
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Q : What is the difference between final, finally and finalize? What do you understand by the java final keyword?

Or

Q : What is final, finalize() and finally?

Or

Q : What is finalize() method?

Or

Q : What is the difference between final, finally and finalize?

Or

Q : What does it mean that a class or member is final?

o final – declare constant
o finally – handles exception
o finalize – helps in garbage collection

Variables defined in an interface are implicitly final. A final class can’t be extended i.e., final class may not be subclassed. This is done for security reasons with basic classes like String and Integer. It also allows the compiler to make some optimizations, and makes thread safety a little easier to achieve. A final method can’t be overridden when its class is inherited. You can’t change value of a final variable (is a constant). finalize() method is used just before an object is destroyed and garbage collected. finally, a key word used in exception handling and will be executed whether or not an exception is thrown. For example, closing of open connections is done in the finally method.
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Q : What is the Java API?

The Java API is a large collection of ready-made software components that provide many useful capabilities, such as graphical user interface (GUI) widgets.
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Q : What is the GregorianCalendar class?

The GregorianCalendar provides support for traditional Western calendars.
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Q : What is the ResourceBundle class?

The ResourceBundle class is used to store locale-specific resources that can be loaded by a program to tailor the program’s appearance to the particular locale in which it is being run.
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Q : Why there are no global variables in Java?

Global variables are globally accessible. Java does not support globally accessible variables due to following reasons:

The global variables breaks the referential transparency
Global variables creates collisions in namespace.
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Q : How to convert String to Number in java program?

The valueOf() function of Integer class is is used to convert string to Number. Here is the code example:
String numString = “1000″;
int id=Integer.valueOf(numString).intValue();
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Q : What is the SimpleTimeZone class?

The SimpleTimeZone class provides support for a Gregorian calendar.
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Q : What is the difference between a while statement and a do statement?

A while statement (pre test) checks at the beginning of a loop to see whether the next loop iteration should occur. A do while statement (post test) checks at the end of a loop to see whether the next iteration of a loop should occur. The do statement will always execute the loop body at least once.
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Q : What is the Locale class?

The Locale class is used to tailor a program output to the conventions of a particular geographic, political, or cultural region.

Describe the principles of OOPS.

There are three main principals of oops which are called Polymorphism, Inheritance and Encapsulation.
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Q : Explain the Inheritance principle.

Inheritance is the process by which one object acquires the properties of another object. Inheritance allows well-tested procedures to be reused and enables changes to make once and have effect in all relevant places
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Q : What is implicit casting?

Implicit casting is the process of simply assigning one entity to another without any transformation guidance to the compiler. This type of casting is not permitted in all kinds of transformations and may not work for all scenarios.

Example

int i = 1000;

long j = i; //Implicit casting
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Q : Is sizeof a keyword in java?

The sizeof operator is not a keyword.
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Q : What is a native method?

A native method is a method that is implemented in a language other than Java.
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Q : In System.out.println(), what is System, out and println?

System is a predefined final class, out is a PrintStream object and println is a built-in overloaded method in the out object.
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Q : What are Encapsulation, Inheritance and Polymorphism

Or

Q : Explain the Polymorphism principle. Explain the different forms of Polymorphism.

Polymorphism in simple terms means one name many forms. Polymorphism enables one entity to be used as a general category for different types of actions. The specific action is determined by the exact nature of the situation.

Polymorphism exists in three distinct forms in Java:
• Method overloading
• Method overriding through inheritance
• Method overriding through the Java interface
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Q : What is explicit casting?

Explicit casting in the process in which the complier are specifically informed to about transforming the object.

Example

long i = 700.20;

int j = (int) i; //Explicit casting
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Q : What is the Java Virtual Machine (JVM)?

The Java Virtual Machine is software that can be ported onto various hardware-based platforms
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Q : What do you understand by downcasting?

The process of Downcasting refers to the casting from a general to a more specific type, i.e. casting down the hierarchy
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Q : What are Java Access Specifiers?

Or

Q : What is the difference between public, private, protected and default Access Specifiers?

Or

Q : What are different types of access modifiers?

Access specifiers are keywords that determine the type of access to the member of a class. These keywords are for allowing
privileges to parts of a program such as functions and variables. These are:
• Public : accessible to all classes
• Protected : accessible to the classes within the same package and any subclasses.
• Private : accessible only to the class to which they belong
• Default : accessible to the class to which they belong and to subclasses within the same package
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Q : Which class is the superclass of every class?

Object.
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Q : Name primitive Java types.

The 8 primitive types are byte, char, short, int, long, float, double, and boolean.
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Q : What is the difference between static and non-static variables?

Or

Q : What are class variables?

Or

Q : What is static in java?

Or

Q : What is a static method?

A static variable is associated with the class as a whole rather than with specific instances of a class. Each object will share a common copy of the static variables i.e. there is only one copy per class, no matter how many objects are created from it. Class variables or static variables are declared with the static keyword in a class. These are declared outside a class and stored in static memory. Class variables are mostly used for constants. Static variables are always called by the class name. This variable is created when the program starts and gets destroyed when the programs stops. The scope of the class variable is same an instance variable. Its initial value is same as instance variable and gets a default value when its not initialized corresponding to the data type. Similarly, a static method is a method that belongs to the class rather than any object of the class and doesn’t apply to an object or even require that any objects of the class have been instantiated.
Static methods are implicitly final, because overriding is done based on the type of the object, and static methods are attached to a class, not an object. A static method in a superclass can be shadowed by another static method in a subclass, as long as the original method was not declared final. However, you can’t override a static method with a non-static method. In other words, you can’t change a static method into an instance method in a subclass.

Non-static variables take on unique values with each object instance.
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Q : What is the difference between the boolean & operator and the && operator?

If an expression involving the boolean & operator is evaluated, both operands are evaluated, whereas the && operator is a short cut operator. When an expression involving the && operator is evaluated, the first operand is evaluated. If the first operand returns a value of true then the second operand is evaluated. If the first operand evaluates to false, the evaluation of the second operand is skipped.
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Q : How does Java handle integer overflows and underflows?

It uses those low order bytes of the result that can fit into the size of the type allowed by the operation.
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Q : What if I write static public void instead of public static void?

Program compiles and runs properly.
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Q : What is the difference between declaring a variable and defining a variable?

In declaration we only mention the type of the variable and its name without initializing it. Defining means declaration + initialization. E.g. String s; is just a declaration while String s = new String (“bob”); Or String s = “bob”; are both definitions.
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Q : What type of parameter passing does Java support?

In Java the arguments (primitives and objects) are always passed by value. With objects, the object reference itself is passed by value and so both the original reference and parameter copy both refer to the same object.
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Q : Explain the Encapsulation principle.

Encapsulation is a process of binding or wrapping the data and the codes that operates on the data into a single entity. This keeps the data safe from outside interface and misuse. Objects allow procedures to be encapsulated with their data to reduce potential interference. One way to think about encapsulation is as a protective wrapper that prevents code and data from being arbitrarily accessed by other code defined outside the wrapper.
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Q : What do you understand by a variable?

Variable is a named memory location that can be easily referred in the program. The variable is used to hold the data and it can be changed during the course of the execution of the program.
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Q : What do you understand by numeric promotion?

The Numeric promotion is the conversion of a smaller numeric type to a larger numeric type, so that integral and floating-point operations may take place. In the numerical promotion process the byte, char, and short values are converted to int values. The int values are also converted to long values, if necessary. The long and float values are converted to double values, as required.
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Q : What do you understand by casting in java language? What are the types of casting?

The process of converting one data type to another is called Casting. There are two types of casting in Java; these are implicit casting and explicit casting.
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Q : What is the first argument of the String array in main method?

The String array is empty. It does not have any element. This is unlike C/C++ where the first element by default is the program name. If we do not provide any arguments on the command line, then the String array of main method will be empty but not null.
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Q : How can one prove that the array is not null but empty?

Print array.length. It will print 0. That means it is empty. But if it would have been null then it would have thrown a NullPointerException on attempting to print array.length.
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Q : Can an application have multiple classes having main method?

Yes. While starting the application we mention the class name to be run. The JVM will look for the main method only in the class whose name you have mentioned. Hence there is not conflict amongst the multiple classes having main method.
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Q : When is static variable loaded? Is it at compile time or runtime? When exactly a static block is loaded in Java?

Static variable are loaded when classloader brings the class to the JVM. It is not necessary that an object has to be created. Static variables will be allocated memory space when they have been loaded. The code in a static block is loaded/executed only once i.e. when the class is first initialized. A class can have any number of static blocks. Static block is not member of a class, they do not have a return statement and they cannot be called directly. Cannot contain this or super. They are primarily used to initialize static fields.
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Q : Can I have multiple main methods in the same class?

We can have multiple overloaded main methods but there can be only one main method with the following signature :

public static void main(String[] args) {}

No the program fails to compile. The compiler says that the main method is already defined in the class.
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Q : Explain working of Java Virtual Machine (JVM)?

JVM is an abstract computing machine like any other real computing machine which first converts .java file into .class file by using Compiler (.class is nothing but byte code file.) and Interpreter reads byte codes.
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Q : How can I swap two variables without using a third variable?

Add two variables and assign the value into First variable. Subtract the Second value with the result Value. and assign to Second variable. Subtract the Result of First Variable With Result of Second Variable and Assign to First Variable. Example:

int a=5,b=10;a=a+b; b=a-b; a=a-b;

An other approach to the same question

You use an XOR swap.

for example:

int a = 5; int b = 10;
a = a ^ b;
b = a ^ b;
a = a ^ b;
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Q : What is data encapsulation?

Encapsulation may be used by creating ‘get’ and ‘set’ methods in a class (JAVABEAN) which are used to access the fields of the object. Typically the fields are made private while the get and set methods are public. Encapsulation can be used to validate the data that is to be stored, to do calculations on data that is stored in a field or fields, or for use in introspection (often the case when using javabeans in Struts, for instance). Wrapping of data and function into a single unit is called as data encapsulation. Encapsulation is nothing but wrapping up the data and associated methods into a single unit in such a way that data can be accessed with the help of associated methods. Encapsulation provides data security. It is nothing but data hiding.
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Q : What is reflection API? How are they implemented?

Reflection is the process of introspecting the features and state of a class at runtime and dynamically manipulate at run time. This is supported using Reflection API with built-in classes like Class, Method, Fields, Constructors etc. Example: Using Java Reflection API we can get the class name, by using the getName method.
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Q : Does JVM maintain a cache by itself? Does the JVM allocate objects in heap? Is this the OS heap or the heap maintained by the JVM? Why

Yes, the JVM maintains a cache by itself. It creates the Objects on the HEAP, but references to those objects are on the STACK.
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Q : What is phantom memory?

Phantom memory is false memory. Memory that does not exist in reality.
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Q : Can a method be static and synchronized?

A static method can be synchronized. If you do so, the JVM will obtain a lock on the java.lang.
Class instance associated with the object. It is similar to saying:

synchronized(XYZ.class) {

}
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Q : What is difference between String and StringTokenizer?

A StringTokenizer is utility class used to break up string.

Example:

StringTokenizer st = new StringTokenizer(“Hello World”);

while (st.hasMoreTokens()) {

System.out.println(st.nextToken());

}

Output:

Hello

World

Thursday, 18 August 2011

Constructor Examples

A java constructor
has the same name as the name of the class to which it belongs.
Constructor’s syntax does not include a return type,
since constructors never return a value.

Constructors may include parameters of various types. When the constructor is invoked using the new operator, the types must match those that are specified in the constructor definition.

Java provides a default
constructor which takes no arguments and performs
no special actions or initializations, when
no explicit constructors are provided.

The only action taken by the implicit default constructor is to call
the superclass constructor using the super() call. Constructor arguments
provide you with a way to provide parameters for the initialization of
an object.

Below is an example of a cube class containing 2 constructors. (one default and one parameterized constructor).

public class Cube1 {



	int length;

	int breadth;

	int height;

	public int getVolume() {

		return (length * breadth * height);

	}

	Cube1() {

		length = 10;

		breadth = 10;

		height = 10;

	}

	Cube1(int l, int b, int h) {

		length = l;

		breadth = b;

		height = h;

	}

	public static void main(String[] args) {

		Cube1 cubeObj1, cubeObj2;

		cubeObj1 = new Cube1();

		cubeObj2 = new Cube1(10, 20, 30);

&amp;amp;amp;lt;font size=-1&amp;amp;amp;gt;

		System.out.println("Volume of Cube1 is : " + cubeObj1.getVolume());

		System.out.println("Volume of Cube1 is : " + cubeObj2.getVolume());

	}

}

Download Cube1.java

Note: If a class defines an explicit constructor, it no longer has a default constructor to set the state of the objects.

If such a class requires a default constructor, its implementation must
be provided. Any attempt to call the default constructor will be a
compile time error if an explicit default constructor is not provided in
such a case.

Java Overloaded Constructors

Like methods, constructors can also be overloaded. Since the
constructors in a class all have the same name as the class, />their
signatures are differentiated by their parameter lists. The above
example shows that the Cube1 constructor is overloaded one being the default constructor and the other being a parameterized constructor.

It is possible to use this() construct, to implement local chaining
of constructors in a class. The this() call in a constructorinvokes the
an other constructor with the corresponding parameter list within the same class. Calling the default constructor to create a Cube object results in the second and third parameterized constructors being called as well. Java requires that any this() call must occur as the first statement in a constructor.

Below is an example of a cube class containing 3 constructors which demostrates the this() method in Constructors context

public class Cube2 {



	int length;

	int breadth;

	int height;

	public int getVolume() {

		return (length * breadth * height);

	}

	Cube2() {

		this(10, 10);

		System.out.println("Finished with Default Constructor");

	}

	Cube2(int l, int b) {

		this(l, b, 10);

		System.out.println("Finished with Parameterized Constructor having 2 params");

	}

	Cube2(int l, int b, int h) {

		length = l;

		breadth = b;

		height = h;

		System.out.println("Finished with Parameterized Constructor having 3 params");

	}

	public static void main(String[] args) {

		Cube2 cubeObj1, cubeObj2;

		cubeObj1 = new Cube2();

		cubeObj2 = new Cube2(10, 20, 30);

		System.out.println("Volume of Cube1 is : " + cubeObj1.getVolume());

		System.out.println("Volume of Cube2 is : " + cubeObj2.getVolume());

	}

}



public class Cube2 {



	int length;

	int breadth;

	int height;

	public int getVolume() {

		return (length * breadth * height);

	}

	Cube2() {

		this(10, 10);

		System.out.println("Finished with Default Constructor");

	}

	Cube2(int l, int b) {

		this(l, b, 10);

		System.out.println("Finished with Parameterized Constructor having 2 params");

	}

	Cube2(int l, int b, int h) {

		length = l;

		breadth = b;

		height = h;

		System.out.println("Finished with Parameterized Constructor having 3 params");

	}

	public static void main(String[] args) {

		Cube2 cubeObj1, cubeObj2;

		cubeObj1 = new Cube2();

		cubeObj2 = new Cube2(10, 20, 30);

		System.out.println("Volume of Cube1 is : " + cubeObj1.getVolume());

		System.out.println("Volume of Cube2 is : " + cubeObj2.getVolume());

	}

}

Output

Finished with Parameterized Constructor having 3 params

Finished with Parameterized Constructor having 2 params

Finished with Default Constructor

Finished with Parameterized Constructor having 3 params

Volume of Cube1 is : 1000

Volume of Cube2 is : 6000

Download Cube2.java

Constructor Chaining

Every constructor calls its superclass constructor. An implied
super() is therefore included in each constructor which does not include
either the this() function or an explicit super() call as its first
statement. The super() statement invokes a constructor of the super
class.

The implicit super() can be replaced by an explicit super(). The super statement must be the first statement of the constructor.

The explicit super allows parameter values to be passed
to the constructor of its superclass and must have matching parameter
types A super() call in the constructor of a subclass will result in
the call of the relevant constructor from the superclass, based on the
signature of the call. This is called constructor chaining.

Below is an example of a class demonstrating constructor chaining using super() method.

class Cube {



	int length;

	int breadth;

	int height;

	public int getVolume() {

		return (length * breadth * height);

	}

	Cube() {

		this(10, 10);

		System.out.println("Finished with Default Constructor of Cube");

	}

	Cube(int l, int b) {

		this(l, b, 10);

		System.out.println("Finished with Parameterized Constructor having

									2 params of Cube");

	}

	Cube(int l, int b, int h) {

		length = l;

		breadth = b;

		height = h;

		System.out.println("Finished with Parameterized Constructor having

									3 params of Cube");

	}

}



public class SpecialCube extends Cube {



	int weight;

	SpecialCube() {

		super();

		weight = 10;

	}

	SpecialCube(int l, int b) {

		this(l, b, 10);

		System.out.println("Finished with Parameterized Constructor having

									2 params of SpecialCube");

	}

	SpecialCube(int l, int b, int h) {

		super(l, b, h);

		weight = 20;

		System.out.println("Finished with Parameterized Constructor having

									3 params of SpecialCube");

	}

	public static void main(String[] args) {

		SpecialCube specialObj1 = new SpecialCube();

		SpecialCube specialObj2 = new SpecialCube(10, 20);

		System.out.println("Volume of SpecialCube1 is : "

				+ specialObj1.getVolume());

		System.out.println("Weight of SpecialCube1 is : "

				+ specialObj1.weight);

		System.out.println("Volume of SpecialCube2 is : "

				+ specialObj2.getVolume());

		System.out.println("Weight of SpecialCube2 is : "

				+ specialObj2.weight);

	}

}

Download SpecialCube.java

Output

Finished with Parameterized Constructor having 3 params of SpecialCube

Finished with Parameterized Constructor having 2 params of SpecialCube

Volume of SpecialCube1 is : 1000

Weight of SpecialCube1 is : 10

Volume of SpecialCube2 is : 2000

Weight of SpecialCube2 is : 20

The super() construct as with this() construct: if used, must occur
as the first statement in a constructor, and it can only be used in a
constructor declaration. This implies that this() and super() calls
cannot both occur in the same constructor. Just as the this() construct
leads to chaining of constructors in the same class, the super()
construct leads to chaining of subclass constructors to superclass
constructors.

if a constructor has neither a this() nor a super() construct as its
first statement, then a super() call to the
default constructor in the superclass is inserted.

Note: If a class only defines non-default
constructors, then its subclasses will not include an implicit
super() call. This will be flagged as a compile-time
error. The subclasses must then explicitly call a
superclass constructor, using the super() construct with the right
arguments to match the appropriate constructor
of the superclass.

Below is an example of a class demonstrating constructor chaining using explicit super() call.

class Cube {



	int length;

	int breadth;

	int height;

	public int getVolume() {

		return (length * breadth * height);

	}

	Cube(int l, int b, int h) {

		length = l;

		breadth = b;

		height = h;

		System.out.println("Finished with Parameterized Constructor having

								3 params of Cube");

	}

}



public class SpecialCube1 extends Cube {



	int weight;

	SpecialCube1() {

		super(10, 20, 30); //Will Give a Compilation Error without this line

		weight = 10;

	}

	public static void main(String[] args) {

		SpecialCube1 specialObj1 = new SpecialCube1();

		System.out.println("Volume of SpecialCube1 is : "+ specialObj1.getVolume());

	}

}

Output

Finished with Parameterized Constructor having 3 params of Cube

Volume of SpecialCube1 is : 6000

How does Java technology relate to dynamic languages and functional programming?

Many aspiring Java developers have a wealth of experience in other languages. And even veteran Java developers appreciate that the Java programming language isn't the ideal language for every development need. Fortunately, the JVM's support for multiple languages lets the Java platform take advantage of the agility and features of modern dynamic scripting languages and functional languages for prototyping or building certain types of applications.
Learn more about it:

The Groovy scripting language puts the features and libraries Java developers are most familiar with in an agile development framework that doesn't require compilation, eases syntactical constructs, and lets its scripts be used inside normal Java applications. Get a comprehensive look at what Groovy can do in the Practically Groovy column series.

The Java scripting API, new in Java SE 6 and backward-compatible to Java SE 5, provides a simple way to invoke dozens of scripting languages using a small set of interfaces and concrete classes. It also lets you read and invoke external scripts at run time, enabling you to change a running application's behavior. Read more about it in the two-part article "Invoke dynamic languages dynamically."

Are you a fan of functional programming? The busy Java developer's guide to Scala column series introduces Scala, a programming language that combines functional and object-oriented techniques for the JVM.

Support for alternative languages has been a JVM feature for quite a while. Check out the alt.lang.jre column series to learn about using implementations of Rexx, Ruby, JavaScript, Python, and other languages on the Java platform.

How does Java technology relate to SOA/web services?

A service-oriented architecture (SOA) is a component model that relates the functional units of an application (services) through well-defined interfaces and contracts between the services. The interface is defined independently of the hardware, operating system, and programming language in which the service is implemented, letting services constructed on different systems interact with one another in a uniform, universal manner. SOAs are a loosely coupled alternative model to more-traditional, tightly coupled, object-oriented models.
The resulting web services let business rules and processes be defined in XML so software applications can communicate in a platform- and programming language-independent manner. XML technology makes data portable and facilitates the creation of messages, while Java technology makes code portable. The fact that XML and the Java language work well together makes them an ideal combination to build and deploy web services.
Learn more about it:

The New to SOA and web services and New to XML pages on developerWorks will help you get oriented in these complex technologies.

The Java web services series explores Java web services frameworks and new layers of functionality built on top of web services.

"Build a RESTful web service" introduces the elegant architectural style called Representational State Transfer (REST) and shows how to use a Java-based framework for building RESTful web services.

JAX-WS is a fundamental technology for developing SOAP-based and RESTful Java web services. The tutorial "Design and develop JAX-WS 2.0 web services" offers a hands-on introduction to this API.

How does Java technology relate to cloud computing?

Cloud computing solutions let their users conveniently access a shared pool of physical or virtual computing resources on demand, typically on a pay-as-you-go basis. The Java ecosystem is expanding to support developers who want to build, test, or deploy Java applications on the cloud.
Learn more about it:

The three-part article "Google App Engine for Java," along with "Java development 2.0: Hello Google App Engine," will get you started quickly with Google's cloud-computing platform for Java developers.

In "Java development 2.0: Gaelyk for Google App Engine," read about a Groovy-based framework that makes rapid development on Google App Engine even faster.

"Java development 2.0: You can borrow EC2 too" and "Java development 2.0: Easy EC2" introduce Amazon's cloud platform and some Java-based tools you can use with it.

Be sure to check out the developerWorks Cloud computing area for many more cloud resources.

How does Java technology relate to web application development?

The Java language has long been a mainstay of web development, and recent years have seen an explosion of Java frameworks and tools that streamline web development and facilitate the creation of rich, interactive Web 2.0 applications.
Learn more about web development in the Java language:

The Mastering Grails column series is a guide to Grails, a modern web development framework written in Groovy. Grails seamlessly integrates legacy Java code while adding the flexibility and dynamism of a scripting language. (For more information about Groovy, see How does Java technology relate to dynamic languages and functional programming?, below.)

Ajax, a programming methodology that uses client-side scripting to exchange data with the web server, enables faster page updates without multiple page reloads. Get a handle on how Ajax applies to you as a Java developer in the multipart article "Ajax and Java development made simpler" and the Ajax for Java developers series. And visit the developerWorks Ajax resource center for lots more on Ajax.

JavaServer Faces (JSF) technology's programming model helps you craft web applications by assembling reusable UI components in a page, connecting these components to an application data source, and wiring client-generated events to server-side event handlers. (See JSF 2 fu for an introduction to the latest JSF version, followed by a series of in-depth articles.)

The Eclipse Web Tools Platform (WTP) extends the popular Eclipse IDE with tools for developing Java EE web applications. (See the tutorial "An introduction to the Eclipse Web Tools Platform V1.0.")

You can also visit the developerWorks Web development zone for many more excellent web application development resources.

How can I improve my Java programming skills?

You can take two routes to improving your skills: enroll in a course (for certification or just for the learning) or teach yourself (and of course, practice by writing code). Besides tapping the knowledge of experienced developers, the coursework or certification path can offer tangible evidence to prospective employers that you have the skills to build the technology they need. And by experimenting on your own and using available resources, you sharpen your skills in various areas of Java technology. The following resources should help either endeavor:

Tutorials and articles

developerWorks offers a world of hands-on Java tutorials — the next-best learning experience to writing the code yourself. For a comprehensive introduction to the Java language, head directly to "Introduction to Java programming, Part 1: Java language basics" and "Introduction to Java programming, Part 2: Constructs for real-world applications."

"Speaking the Java language without an accent" will help you program fluently when you adopt the Java language.

Check out the 5 things you didn't know about ... series to fine-tune your Java knowledge as you master the fundamentals.

Translating design theory into practical application(s) is the focus of the Java theory and practice series. The "Testing with leverage" and "Kill bugs dead" articles in this series, for example, offer essential guidance on designing applications with integrated testing and bug detection.

The Taming Tiger series is an excellent reference for sharpening your Java programming claws.

Books, websites, and events

No better place to start than with "Essential Java resources," a comprehensive listing of must-have books, sites, blogs, events, and more.

Check out the Java technology zone's Events page to find conferences, seminars, workshops, and webcasts relevant to Java developers.

Games

Robocode is an easy-to-use robotics battle simulator built on Java technology that teaches you to program while providing hours of pure entertainment. For an introduction to Robocode, read "Rock 'em, sock 'em Robocode!" and check out "Secrets from the Robocode masters: A collection of hints, tips, and advice from the Robocode masters."

CodeRuler, CodeRally, and CodeInvaders Challenge are Java-based, real-time programming games based on the Eclipse platform.

IBM technical training

Choose among a wide variety of online, classroom, and multimedia-based Java courses offered by IBM Global Services.

Certification training

IBM offers professional certification in such related technologies as WebSphere® development (for enterprise Java applications), IBM Rational® software, DB2®, XML, and SOA.

Forums

For an even more interactive approach to learning how to use the Java language, dive into the Java discussion forums, moderated by noted experts with years of real-world experience in crafting Java-related technology.

How does Java technology relate to open source software development?

Open source software is an integral part of Java software development. Myriad third-party open source projects extend Java technology with libraries, tools, frameworks, applications, and application servers to help programmers harness this powerful technology. Many of the technologies discussed in this article are open source.

OpenJDK

OpenJDK is a free and open source implementation of the Java programming language, available under the GPLv2 license. In October 2010, IBM, previously the main corporate contributor of the competing Apache Harmony project, formed an alliance with Oracle to support OpenJDK and create a single, stable platform for Java development.
The OpenJDK community is currently focused on the next major revision of the Java platform, Java 7, which is expected to include a number of the features noted in "A new era in Java technology" (some will likely end up in Java 8 per Oracle's latest roadmap) and the two-part article, "An NIO.2 primer."

Apache

The Apache Software Foundation is the umbrella organization for a panoply of open source projects that are predominantly Java language-based. Here's a sampling:

Apache Ant is the de facto standard build tool for Java development. (See the tutorial "Apache Ant 101: Make Java builds a snap" and "Invoking Apache Ant programmatically.")

The Apache Maven build tool is designed to meet the challenges of modern software projects that require dynamic collaboration among project teams and depend on a mix of globally created and maintained components. (See the tutorial "Introduction to Apache Maven 2" and the article "5 things you didn't know about ... Apache Maven")

Get acquainted with two Apache web services frameworks in "Java web services: Introducing CXF" and "Web services and Axis2 architecture."

Read "Using Apache Lucene to search text" to learn about Apache's full-featured text search-engine library.

"Introducing Apache Mahout" introduces an Apache project that's building scalable, machine-learning libraries.

Apache Tomcat is a popular web container that supports servlets and JavaServer Pages technology. (The tutorial "Tomcat for beginning web developers" will help you get started with Tomcat.)

The Apache Geronimo project is building a fully compliant Java EE application server based entirely on open source components. (Meet Geronimo in "Get started with Geronimo" and visit the developerWorks Apache Geronimo project resources for a wealth of Geronimo information.)

Apache Derby is a relational database implemented entirely in the Java language. (Get started with "Developing with Apache Derby — Hitting the Trifecta: Introduction to Apache Derby" and visit the developerWorks Apache Derby project resources for tons more on Derby.)

Eclipse

Eclipse is a vendor-neutral, open development platform and set of application frameworks for building software. The Eclipse platform is written in the Java language and provides a plug-in based framework that makes it easier to create, integrate, and use software tools. (IBM is a founding member of Eclipse and actively participates on the Eclipse.org Board of Stewards and its working subcommittees.) Learn more about some of the platform's component technologies for Java development:

"A tour of Eclipse Helios" gives you a look at the latest simultaneous release of multiple Eclipse projects.

Read "Eclipse e4 highlights" to learn what's coming in the next generation of the Eclipse platform.

AspectJ is an aspect-oriented extension to the Java language that can be used to modularize crosscutting concerns such as logging and exception handling. (See the tutorial "An introduction to AOP" and explore further in several articles in the AOP at work series.)

The Standard Widget Toolkit (SWT) is a user interface toolkit designed to provide efficient, portable access to the UI facilities of the underlying operating system. (See "A gentle introduction to SWT and JFace: How to create a simple SWT application.")

Mylyn is a sophisticated task tracker for Eclipse users. (See "Mylyn 2.0, Part 1: Integrated task management" and "Mylyn 2.0, Part 2: Automated context management"" for a comprehensive Mylyn guide.

The Eclipse Test and Performance Tools Platform (TPTP) supplies frameworks and services for test and performance tools. (See the tutorial "Introduction: Eclipse Test and Performance Tools Platform.")

The Eclipse Web Tools Platform (WTP) extends the Eclipse platform with tools for developing Java EE web applications. (See the tutorial "An introduction to the Eclipse Web Tools Platform V1.0.")

Visit the developerWorks Eclipse IDE project resources for loads more Eclipse articles and tutorials.

Spring

The popular Spring framework is a layered framework for Java EE application development:

Check out The Spring series and the tutorial "Introduction to Spring 2 and JPA" for detailed information.

Spring Security — formerly known as the Acegi Security System for Spring — is a powerful, flexible security solution for enterprise applications developed using the Spring framework. Learn more in the four-part article "Securing Java applications with Acegi."

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Tuesday, 10 April 2012

Thursday, 18 August 2011

Java Overloaded Constructors

Constructor Chaining