Doubt on interface

[Martin Arun Paul Perumala]

The following code is simple trying to take 2 variables and adding, substracting and multiplying them using interface concept.

In the demo class I want to use "function chaining" like a1.setdata().add().sub().mul(). Is it possible? I tried to do it but I guess we have to create another class. please help me

Thank you

interface calculate
  {
  void add();
   void sub();
   void mul();
 
  }

class A implements calculate
  {
  int x,y;
 public  void setdata()
  {
        x=10;
y=34;

  }
 
  public  void add()
  {
 int z;
 z=x+y;
 System.out.println("the added sum is :" +z);
    
  }
  public  void sub()
  {
  int z;
  z=y-x;
  System.out.println("the substracted value is :" +z);
     
  }
 
  public  void mul()
  {
  int z;
  z=x*y;
  System.out.println("the multipied value is :" +z);
    
  }
  }

class demo
 {
public static void main(String[] args) 
{
A a1= new A();
 
a1.setdata();
a1.add();
a1.sub();
a1.mul();
 

}
 
}

[edit]Add code tags. CR[/edit]
[ December 13, 2008: Message edited by: Campbell Ritchie ]

[Ulf Dittmer]

If you want to chain methods, then they can't be "void" - in other words, return nothing. They should return the result of the previous calculation - what in the code is stored in "z".

There's no point really in using an interface here. You could use one if all the individual operations (plus, minus, multiply, ...) each had their own class; but that would be a contrived use.
[ December 13, 2008: Message edited by: Ulf Dittmer ]

[Martin Arun Paul Perumala]

so can we change the return type (void) of the methods in the interface class to something else like object type.?

[Rob Spoor]

Take a look at java.lang.StringBuilder. After modifying its contents, it returns "this":

public StringBuilder append(String string)
{
    // append string here
    return this;
}

Of course you can do the same if you want to keep your contents fixed. In that case, take a look at java.math.BigInteger. A few examples:

public BigInteger add(BigInteger val)
{
    // calculate value
    return new BigInteger(value);
}
 
public BigInteger multiply(BigInteger val)
{
    // calculate value
    return new BigInteger(value);
}

Both can now be chained:

StringBuilder builder = new StringBuilder().append("Hello ").append("World").append("!");
BigInteger big = new BigInteger("5").add(new BigInteger("6")).multiply(new BigInteger("7"));

The first line creates one single StringBuilder object that has three strings appended to it.
The second line creates 5 BigInteger objects:
- new BigInteger("5")
- new BigInteger("6")
- the result of 5 + 6
- new BigInteger("7")
- the result of (5 + 6) * 7

In the end, "big" will contain a value of 77.