[JAVA] INNER CLASS - 내부 클래스

 

내부 클래스

- outter class의 멤버를 자유롭게 씀 -> 확장

- static 필드를 쓸 목적

 

1. member inner class

public class MemberInner { //초기화 시켜주면 안되지만 확인을 위해 초기화
    private int a = 10;
    public int b = 20;
    protected static int c = 30;
    
    class Member{ //Inner class
        public void disp() {
            System.out.println(a);
            System.out.println(b);
            System.out.println(c);
        }
    }
    
    public static void main(String[] args) {
        //MemberInner mi = new MemberInner();
        //MemberInner.Member m = mi.new Member();
        MemberInner.Member m = new MemberInner().new Member();
        m.disp();
    }
}

 

2. static inner class : 외부 마음대로 접근 못함

public class MemberInner {
    private int a = 10;
    public int b = 20;
    protected static int c = 30;
    
    static class Member{ //Static Inner class
        public void disp() {
            //System.out.println(a);
            //System.out.println(b);
            System.out.println(c);
        }
    }
    
    public static void main(String[] args) {
        MemberInner.Member m = new MemberInner.Member();
        m.disp();
    }
}

 

3. local inner class : 클래스 안에 있는 특정 메소드 안에 클래스를 생성 할 수 있다

public class MemberInner {
    private int a = 10;
    public int b = 20;
    protected static int c = 30;

    public void output() {
        class Member { // Local Inner Class
            public void disp() {
                System.out.println(a);
                System.out.println(b);
                System.out.println(c);
            }
        }
        //output()안에 있는 Member 클래스 선언
        Member m = new Member();
        m.disp();
    }

    public static void main(String[] args) {
        MemberInner mi = new MemberInner();
        mi.output();
    }
}

 

4. anonymous inner class : 익명 - 1회용 ex) 이벤트 처리

abstract class Abs {
    abstract void disp();
}

public class MemberInner {
    private int a = 10;
    public int b = 20;
    protected static int c = 30;

    public Abs abs = new Abs() {
        @Override
        void disp() {
            System.out.println(a);
            System.out.println(b);
            System.out.println(c);
        }
    };

    public static void main(String[] args) {
        MemberInner mi = new MemberInner();
        mi.abs.disp();
    }
}

 

---

 

예시 

import java.awt.*;
import java.awt.event.*;

class WindowHandler extends WindowAdapter {
    public void windowClosing(WindowEvent e) {
        System.exit(0);
    }
}

class KeyEventHandler extends KeyAdapter {
    //member inner class
    TextField tf;
    TextArea ta;
    public KeyEventHandler(TextField tf, TextArea ta) {
        //call by address로 연결
        this.tf = tf;
        this.ta = ta;
    }

    public void keyTyped(KeyEvent e) {
        if (e.getKeyChar() == KeyEvent.VK_ENTER) {
            ta.append(tf.getText() + "\n");
            tf.setText("");
        }
    }
}

public class AnonymousEx extends Frame implements ActionListener {
    //anonymous inner class
    Panel p1, p2, p3;
    TextField tf;
    TextArea ta;
    Button b1, b2;

    public AnonymousEx() {
        super("Adapter 테스트");
        p1 = new Panel();
        p2 = new Panel();
        p3 = new Panel();
        
        tf = new TextField(35);
        ta = new TextArea(10, 35);
        
        b1 = new Button("Clear");
        b2 = new Button("Exit");

        p1.add(tf);
        p2.add(ta);
        p3.add(b1);
        p3.add(b2);

        add("North", p1);
        add("Center", p2);
        add("South", p3);
        setBounds(300, 200, 300, 300);

        setVisible(true);

        b1.addActionListener(this);
        b2.addActionListener(this);
        
        tf.addKeyListener(new KeyEventHandler(tf, ta));
        addWindowListener(new WindowHandler());
    }

    public void actionPerformed(ActionEvent e) {
        String str = e.getActionCommand();
        if (str.equals("Clear")) {
            ta.setText("");
            tf.setText("");
            tf.requestFocus();
        }
        else if (str.equals("Exit")) {
            System.exit(0);
        }
    }

    public static void main(String[] args) {
        AnonymousEx ae = new AnonymousEx();
    }
}

 

위의 코드을 anonymous inner class를 사용하여 구현

import java.awt.*;
import java.awt.event.*;

public class AnonymousInner extends Frame implements ActionListener {
    Panel p1, p2, p3;
    TextField tf;
    TextArea ta;
    Button b1, b2;

    public AnonymousInner() {
        super("Adapter 테스트");
        p1 = new Panel();
        p2 = new Panel();
        p3 = new Panel();
        tf = new TextField(35);
        ta = new TextArea(10, 35);
        b1 = new Button("Clear");
        b2 = new Button("Exit");

        p1.add(tf);
        p2.add(ta);
        p3.add(b1);
        p3.add(b2);

        add("North", p1);
        add("Center", p2);
        add("South", p3);

        setBounds(300, 200, 300, 300);
        setVisible(true);
        b1.addActionListener(this);
        b2.addActionListener(this);
            
        // anonymous inner class - keyEventHandler
        tf.addKeyListener(new KeyAdapter() {
            public void keyTyped(KeyEvent e) {
                if (e.getKeyChar() == KeyEvent.VK_ENTER) {
                    ta.append(tf.getText() + "\n");
                    tf.setText("");
                }
            }
        });

        // anonymous inner class - windowHandler
        addWindowListener(new WindowAdapter() {
            public void windowClosing(WindowEvent e) { // 재정의해서 알아서 부르게끔 해줌
                System.exit(0);
            }
        });
    }

    public void actionPerformed(ActionEvent e) {
        String str = e.getActionCommand();
        if (str.equals("Clear")) {
            ta.setText("");
            tf.setText("");
            tf.requestFocus();
        } else if (str.equals("Exit")) {
            System.exit(0);
        }
    }

    //keyEventHandler 원래 코드
    /*
     * class KeyEventHandler extends KeyAdapter { //ta, tf를 직접 접근 가능 public void
     * keyTyped(KeyEvent e) { if (e.getKeyChar() == KeyEvent.VK_ENTER) {
     * ta.append(tf.getText() + "\n"); tf.setText(""); } } }
     */

    // Member inner class - keyEventHandler
    /*
     * class KeyEventHandler extends KeyAdapter { public void keyTyped(KeyEvent e) {
     * if (e.getKeyChar() == KeyEvent.VK_ENTER) { ta.append(tf.getText() + "\n");
     * tf.setText(""); } } }
     */

    public static void main(String[] args) {
        new AnonymousInner();
    }
}