내부클래스 설명

MyMain_LocalInner.java
MyMain_MemberInner.java
MyMain_MemberInner2.java

첫 번째 설명
코드가 길어지면서 필요없는 메서드 까지 다 선언해야 오류가 안뜸

package mymain;

import java.awt.event.WindowEvent;
import java.awt.event.WindowListener;

import javax.swing.JFrame;

//  awt ->확장 -> swing
//  Frame         JFrame

public class MyMain_MemberInner extends JFrame {
	
    //멤버로써의 내부클래스
	//윈도우 이벤트 처리객체
	class MyWindowListener implements WindowListener
	{

		@Override
		public void windowOpened(WindowEvent e) {
			// TODO Auto-generated method stub
			
		}

		@Override
		public void windowClosing(WindowEvent e) {
			// TODO Auto-generated method stub
			System.exit(0);
		}

		@Override
		public void windowClosed(WindowEvent e) {
			// TODO Auto-generated method stub
			
		}

		@Override
		public void windowIconified(WindowEvent e) {
			// TODO Auto-generated method stub
			
		}

		@Override
		public void windowDeiconified(WindowEvent e) {
			// TODO Auto-generated method stub
			
		}

		@Override
		public void windowActivated(WindowEvent e) {
			// TODO Auto-generated method stub
			
		}

		@Override
		public void windowDeactivated(WindowEvent e) {
			// TODO Auto-generated method stub
			
		}
		
	}
//------------------------------------------------------------------	

	public MyMain_MemberInner() {
		// TODO Auto-generated constructor stub
		super("내가만든 윈도우");

		//위치
		//this.setLocation(200, 100);
		//크기지정
		//this.setSize(400, 300);

		// 위치 + 크기정보
		this.setBounds(200, 100, 400, 300);

		//보여줘라
		this.setVisible(true);

		//종료코드
		//this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		
		this.addWindowListener(new MyWindowListener());

	}

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		new MyMain_MemberInner();
	}

}

두 번째 설명
자주 사용할 목적으로 선언 형식

package mymain;

import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import java.awt.event.WindowListener;

import javax.swing.JFrame;

//  awt ->확장 -> swing
//  Frame         JFrame

public class MyMain_MemberInner2 extends JFrame {

	//윈도우 이벤트 처리객체
	class MyWindowAdapter extends WindowAdapter
	{
		@Override
		public void windowClosing(WindowEvent e) {
			// TODO Auto-generated method stub
			System.exit(0);
		}
	}
	
	public MyMain_MemberInner2() {
		// TODO Auto-generated constructor stub
		super("내가만든 윈도우");

		// 위치 + 크기정보
		this.setBounds(200, 100, 400, 300);

		//보여줘라
		this.setVisible(true);

		//종료코드
		//this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		WindowListener listener = new MyWindowAdapter();
		this.addWindowListener(listener);
		

	}

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		new MyMain_MemberInner2();
	}

}

간략한코드 
package mymain;

import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;

import javax.swing.JFrame;

//  awt ->확장 -> swing
//  Frame         JFrame

public class MyMain_LocalInner extends JFrame {

	public MyMain_LocalInner() {
		// TODO Auto-generated constructor stub
		super("내가만든 윈도우");

		
		// 위치 + 크기정보
		this.setBounds(200, 100, 400, 300);

		//보여줘라
		this.setVisible(true);

		//종료코드
		//this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		//이벤트처리객체 선언
		class MyWindowAdapter extends WindowAdapter
		{
			@Override
			public void windowClosing(WindowEvent e) {
				// TODO Auto-generated method stub
				System.exit(0);
			}
		}
		
		this.addWindowListener(new MyWindowAdapter());
		

	}

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		new MyMain_LocalInner();
	}

}