Programming with Constructors in Java

In the previous section, I covered the concept of a default constructor in Java.  Now, I shall extend the same with “constructors with parameters” in this section.  Let us go through the code first. 

Now, open your previous application (or download it from my previous articles) and open “MyCalc.java.”  Modify your code so that it looks something like the following:

  public class MyCalc {

    int x;
    int y;

    public MyCalc(int m, int n) {
        x=m;
        y=n;
    }

    public void setValues(int m, int n) {
        x = m;
        y = n;
    }

    public int getSum() {
        int z;
        z = x + y;
        return z;
    }

  }

Now, go back to the frame “test.java.”  Double click on it to open, and finally double click on the button to open source view.  Within the source view, modify your “buttonActionPerformed” in such a way that it looks like the following:

  private void btnShowActionPerformed(java.awt.event.ActionEvent evt) {
  // TODO add your handling code here:
        MyCalc obj1 = new MyCalc(10,20);
        int r;
        r = obj1.getSum();
        this.lblMsg.setText("Sum = " + String.valueOf(r));

    }      

Once you execute your application and click the button, you should be able to see “Sum=30” as the result.  If you examine the “MyCalc” class, you will see that I made the following changes:

    public MyCalc(int m, int n) {
        x=m;
        y=n;
    }

It is basically a constructor (as its name is the same as the class name) which accepts two parameters.  It is automatically executed when an instance/object of the class “MyCalc” is created by sending two integer values as follows:

        MyCalc obj1 = new MyCalc(10,20);

The rest is very similar to the previous explanation.