类之间的相互继承

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public class Demo {
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    public static void main(String[] args) {
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       StringBuffer buf = new  StringBuffer();
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       for(int x = 'a'; x <'z'; x ++){
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           buf.append((char) x);
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       }
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       buf.reverse().delete(0, 5);
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       System.out.println(buf);
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    }
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}

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package cn.cccc.demo;
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import java.util.Arrays;
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import java.util.Random;
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class NumberFactory{
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    private static Random random = new  Random();
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    public static int [] create(int len ){
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       int data []  = new int [len];
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       int foot = 0;
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       while(foot < data.length){
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           int num = random.nextInt(30);
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           data[foot++] = num;
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       }
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       return data;
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    }
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}
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public class Demo {
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    public static void main(String[] args) {
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       int result []  =  NumberFactory.create(5);
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       System.out.println(Arrays.toString(result));
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    }
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}

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package cn.cccc.demo;
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import java.util.Arrays;
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import java.util.Random;
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class Coin {
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    private static Random random = new  Random();
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    private int front;
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    private int back;
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    public void throwCoin(int count){
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       for(int x= 0; x < count ; x++){
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           int side = random.nextInt(2);
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           if(side == 0 ){
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               this.front++;
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           }else {
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               this.back++;
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           }
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       }
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    }
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    public int getFront(){
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       return this.front;
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    }
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    public int getBack(){
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       return this.back;
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    }
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}
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public class Demo {
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    public static void main(String[] args) {
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       Coin coin  = new Coin();
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       coin.throwCoin(1000);
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       System.out.println("正面的次数"+coin.getFront()+"，背面的次数"+coin.getBack());
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    }
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}