CareerCup

Make your class and instance variable as final, your class will be immutable.

public final class Immutable {
	private final String s;
	
	public Immutable(String a){
		s = a;
	}

}

Don't provide public methods that will change your object.
In case of modification, return a new instance.
Prefer to declare your variables as final.
Process everything needed in the constructor.

Example:

public class DoTheMath {
	private int x;
	private int z;

	public DoTheMath(int N) {
		calculate(N);
	}

	private void calculate(int N) {
		// code code code
	}

	public int getX() {
		return this.x;
	}

	public int getZ() {
		return this.z;
	}
}

public final class ImmutableDemo{
private final String panNumber;

public ImmutableDemo(String panNumber){
this.panNumber = panNumber;
}

public getPanumber(){
return panNumber
}
}