A Closer Look at Methods and Classes - Returning Objects

(Page 5 of 12 )

A method can return any type of data, including class types that you create. For example, in the following program, the incrByTen( ) method returns an object in which the value of a is ten greater than it is in the invoking object.

// Returning an object.
class Test {
  int a;
  Test(int i) {
    a = i;
  }
  Test incrByTen() {
    Test temp = new Test(a+10);
    return temp;
  }
}
class RetOb {
  public static void main(String args[]) {
    Test ob1 = new Test(2);
    Test ob2;
    ob2 = ob1.incrByTen();
    System.out.println("ob1.a: " + ob1.a); 
    System.out.println("ob2.a: " + ob2.a);
    ob2 = ob2.incrByTen();
    System.out.println("ob2.a after second increase: "
                        + ob2.a);
  }
}

The output generated by this program is shown here:

ob1.a: 2
ob2.a: 12
ob2.a after second increase: 22

As you can see, each time incrByTen( ) is invoked, a new object is created, and a reference to it is returned to the calling routine.

The preceding program makes another important point: Since all objects are dynamically allocated using new, you don’t need to worry about an object going out-of-scope because the method in which it was created terminates. The object will continue to exist as long as there is a reference to it somewhere in your program. When there are no references to it, the object will be reclaimed the next time garbage collection takes place.

Next: Recursion >>
 

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This article is excerpted from chapter 7 of Java: the Complete Reference, J2SE 5 Edition, written by Herbert Schildt (McGraw-Hill/Osborne, 2004; ISBN: 0072230738). Check it out at your favorite bookstore. Buy this book now.