scoping.java

金旭亮的java教案

// Fig. 6.10: Scoping.java
// A scoping example
import java.awt.Container;
import javax.swing.*;

public class Scoping extends JApplet {
   JTextArea outputArea;
   int x = 1;      // instance variable

   public void init()
   {
      outputArea = new JTextArea();
      Container c = getContentPane();
      c.add( outputArea );
   }

   public void start()
   {
      int x = 5;   // variable local to method start

      outputArea.append( "local x in start is " + x );

      methodA();   // methodA has automatic local x
      methodB();   // methodB uses instance variable x
      methodA();   // methodA reinitializes automatic local x
      methodB();   // instance variable x retains its value

      outputArea.append( "\n\nlocal x in start is " + x );
   }

   public void methodA()
   {
      int x = 25;  // initialized each time a is called

      outputArea.append( "\n\nlocal x in methodA is " + x +
                          " after entering methodA" );
      ++x;
      outputArea.append( "\nlocal x in methodA is " + x +
                          " before exiting methodA" );
   }

   public void methodB()
   {
      outputArea.append( "\n\ninstance variable x is " + x +
                          " on entering methodB" );
      x *= 10;
      outputArea.append( "\ninstance variable x is " + x +
                          " on exiting methodB" );
   }
}   

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