抽象类的作用

http://xyiyy.iteye.com/blog/359362

1. 首先定义一个抽象类，在类中定义了start()方法，其中实现了比大小的规则，但并没有实现如何取得使用者输入和信息的显示方式，只先定义了抽象方法showMessage()与getUserInput()。

{
    private int number;

    public void setNumber(int number)
    {
        this.number = number;
    }

    public void start()
    {
        showMessage("欢迎");
        int guess = 0;
        do{
            guess = getUserInput();
            if(guess > number)
            {
                showMessage("输入的数字较大");
            }
            else if(guess < number)
            {
                showMessage("输入的数字较小");
            }
            else
                showMessage("猜中了");
        }while(guess != number);
    }

    protected abstract void showMessage(String message);
    protected abstract int getUserInput();
}

public abstract class AbstractGuessGame
{
	private int number;

	public void setNumber(int number)
	{
		this.number = number;
	}

	public void start()
	{
		showMessage("欢迎");
		int guess = 0;
		do{
			guess = getUserInput();
			if(guess > number)
			{
				showMessage("输入的数字较大");
			}
			else if(guess < number)
			{
                showMessage("输入的数字较小");
			}
			else
				showMessage("猜中了");
		}while(guess != number);
	}

	protected abstract void showMessage(String message);
	protected abstract int getUserInput();
}

2.使用AbstractGuessGame类的办法是扩展它，并实现其中的抽象方法。如下面的TextModeGame类：

import java.util.Scanner;

public class TextModeGame extends AbstractGuessGame
{
    private Scanner scanner;

    public TextModeGame()
    {
         scanner = new Scanner(System.in);
    }

    protected void showMessage(String message)
    {
        for(int i = 0; i < message.length()*2;i++)
            System.out.print("*");
        System.out.println("\n" + message);
        for(int i = 0; i < message.length()*2;i++)
            System.out.print("*");
    }

    protected int getUserInput()
    {
        System.out.print("\n请输入数字：");
        return scanner.nextInt();
    }
}

import java.util.Scanner;

public class TextModeGame extends AbstractGuessGame
{
	private Scanner scanner;

	public TextModeGame()
	{
         scanner = new Scanner(System.in);
	}

    protected void showMessage(String message)
	{
		for(int i = 0; i < message.length()*2;i++)
			System.out.print("*");
		System.out.println("\n" + message);
		for(int i = 0; i < message.length()*2;i++)
			System.out.print("*");
	}

    protected int getUserInput()
	{
		System.out.print("\n请输入数字：");
		return scanner.nextInt();
	}
}

3.启动游戏的示范类：  

{
    public static void main(String[] args)
    {
         AbstractGuessGame guessGame = new TextModeGame();
         guessGame.setNumber(50);
         guessGame.start();
    }
}