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Inner class

Inner class. Static inner class. 範例 程式 1: public class InnerClass1 {   static  int  i;   final  int  j = 1; int  k;   public static void main(String[]  args ) { Nested n = new Nested(); n.amethod ();   } static class Nested {     public void  amethod () {

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Inner class

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  1. Inner class

  2. Static inner class 範例程式1: public class InnerClass1 {   static int i;   final int j = 1; int k;   public static void main(String[] args) { Nested n = new Nested(); n.amethod();   } static class Nested {     public void amethod() { System.out.println("i = " + i); System.out.println("j = " + j); System.out.println("k = " + k);     }   } } • Static inner class: • 只能存取外部類別的static field • Inner class 有static 關鍵字 可以如何修改?? • "InnerClass1.java": Error #: 308 : non-static variable j cannot be referenced from a static context • "InnerClass1.java": Error #: 308 : non-static variable k cannot be referenced from a static context

  3. MEMBER INNER CLASSES 範例程式2: public class InnerClass2 {   static int i = 10;   final int j = 1; int k;   public static void main(String[] args) { Nested c = new InnerClass2().new Nested(); c.amethod();   }  class Nested {     public void amethod() { System.out.println("i = " + i); System.out.println("j = " + j); System.out.println("k = " + k);     }   } } • Member inner classes: • 能存取外部類別的所有field • Inner class 沒有static 關鍵字 執行結果: i = 10 j = 1 k = 0

  4. LOCAL INNER CLASSES public class InnerClass3 {    public static void main(String[] args) {     InnerClass3 in = new InnerClass3(); in.amethod();   }   public void amethod() {     final staticint i = 100; finalint j = 10;     class NestedC {       public void bmethod() { System.out.println("i = " + i); System.out.println("j = " + j);       }     }     new NestedC().bmethod();   } } • Local inner classes • 宣告在method中的類別，故Local inner classes 不能有static，也不能有modifier(public、protected 、private) • 可以存取外部類別的所有變數，但是不能存取method的local變數 "InnerClass3.java": Error #: 480 : local variable j is accessed from within inner class; needs to be declared final

  5. ANONYMOUS INNER CLASSES • 沒有名稱的類別，匿名類別最常用在event的處理上

  6. import java.awt.*; import java.awt.event.*; public class InnerClass4 extends Frame {   public InnerClass4() {     Button b = new Button("Click me!"); b.addActionListener(       new ActionListener() {         public void actionPerformed(ActionEvent e) { System.out.println("Click me!");         }       }     ); this.add(b); this.setSize(200, 100); this.show(); }   public static void main(String[] args) {     InnerClass4 in = new InnerClass4();   } } • anonymous inner class : • overriding methods • 存取外部類別的所有變數

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