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Constructor

Java ArrayList Constructors

Submitted by Andr on Thu, 10/28/2010 - 00:50

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ArrayList Constructors

1) ArrayList()
Creates an empty ArrayList.

Example
ArrayList arrayList = new ArrayList();

2) ArrayList(int capacity)
Creates an ArrayList with specified initial capacity.

Example
ArrayList arrayList = new ArrayList(10);

3) ArrayList(Collection c)

String Constructors

Submitted by Andr on Wed, 10/27/2010 - 19:21

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String Constructors

String class provides various types of constructors to create String objects. Some of them are,

String()
Creates a new String object whose content is empty i.e. "".

What will happen when you compile and run the following code?

Submitted by Megha on Sat, 09/04/2010 - 18:24

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public class BooleanDemo {
    public static void main(String args[]){
        Boolean bObj = new Boolean("Hello World!");
        System.out.println(bObj);
    }
}

a. Program will not compile
b. Program will throw runtime error
c. Program will print false
d. Program will print true

Answer:

How to call super class constructor from subclass constructor?

Submitted by Bharat on Sat, 09/04/2010 - 00:15

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Constructor of the super class can be called using super.

How to call a constructor from another constructor within the class?

Submitted by Bharat on Sat, 09/04/2010 - 00:14

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Different constructor of the same class can be called using “this”. e.g.

public class Q1 {
 Q1(){
  System.out.println("Default Constructor");
 }
 
 Q1(String msg){
  this(); //calls default constructor
  System.out.println("One Argument Constructor");
 }
}

What happens if you create one argument constructor and do not create constructor without argument?

Submitted by Bharat on Sat, 09/04/2010 - 00:13

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If class does not define any constructors, Java automatically creates default constructor with no arguments. However, if constructor with arguments is specified, Java does not create default one.

Nothing happens if we do not specify the default constructor. However,

What is difference between method and constructor?

Submitted by Bharat on Sat, 09/04/2010 - 00:12

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Constructor is a special member function of a class which is used to create object of that class. Constructor has a same name as that of the class. It also does not have any return type. However, constructor may have arguments.