Constructor overloading
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Constructor Overloading. One context in which you will regularly need to use overloading is when you write constructors for your classes. Constructors are methods that can be overloaded, just like any other method in a class.

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Constructor Overloading

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Constructor Overloading

  • One context in which you will regularly need to use overloading is when you write constructors for your classes.

  • Constructors are methods that can be overloaded, just like any other method in a class.

  • In most situations, you will want to generate objects of a class from different sets of initial defining data:

tMyn


package TimoSoft;

public class MyClass

{

int x;

MyClass()

{

System.out.println("Inside MyClass() constructor.");

x=0;

}

MyClass(int i)

{

System.out.println("Inside MyClass(int) constructor.");

x=i;

}

tMyn


MyClass(double d)

{

System.out.println("Inside MyClass(double) constructor.");

x=(int)d;

}

void getXvalue()

{

System.out.println("The value of the instance variable \nof the object "

+this+" is "+x+".");

}

}

tMyn


package TimoSoft;

public class MyClassTest

{

public static void main(String[] args)

{

MyClass first=new MyClass();

MyClass second=new MyClass(52);

MyClass third=new MyClass(13.6);

first.getXvalue();

second.getXvalue();

third.getXvalue();

}

}

tMyn


run:

Inside MyClass() constructor.

Inside MyClass(int) constructor.

Inside MyClass(double) constructor.

The value of the instance variable

of the object TimoSoft.MyClass@19821f is 0.

The value of the instance variable

of the object TimoSoft.MyClass@addbf1 is 52.

The value of the instance variable

of the object TimoSoft.MyClass@42e816 is 13.

BUILD SUCCESSFUL (total time: 1 second)

tMyn


  • One common reason that constructors are overloaded is to allow one object to initialize another.

  • The need to produce an identical copy of an object occurs often:

tMyn


package TimoSoft;

public class MyClass

{

int x, y;

MyClass()

{

System.out.println("Inside MyClass() constructor.");

x=0;

y=0;

}

MyClass(int i, int j)

{

System.out.println("Inside MyClass(int) constructor.");

x=i;

y=j;

}

tMyn


MyClass(MyClass obj)

{

System.out.println("Inside MyClass(MyClass) constructor.");

x=obj.x;

y=obj.y;

}

void getXYvalues()

{

System.out.println("The value of the instance variables \nof the object "

+this+" are "+x+" and "+y+".");

}

}

tMyn


package TimoSoft;

public class MyClassTest

{

public static void main(String[] args)

{

MyClass first=new MyClass();

MyClass second=new MyClass(52, 18);

MyClass third=new MyClass(second);

first.getXYvalues();

second.getXYvalues();

third.getXYvalues();

}

}

tMyn


run:

Inside MyClass() constructor.

Inside MyClass(int) constructor.

Inside MyClass(MyClass) constructor.

The value of the instance variables

of the object TimoSoft.MyClass@19821f are 0 and 0.

The value of the instance variables

of the object TimoSoft.MyClass@addbf1 are 52 and 18.

The value of the instance variables

of the object TimoSoft.MyClass@42e816 are 52 and 18.

BUILD SUCCESSFUL (total time: 1 second)

tMyn


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