Java多線程通信之兩個線程分別打印AB各10次

一道經典的面試題目：兩個線程，分別打印AB，其中線程A打印A，線程B打印B，各打印10次，使之出現ABABABABA.. 的效果

package com.shangshe.path;

public class ThreadAB {

    /**
     * @param args
     */
    public static void main(String[] args) {
        
        final Print business = new Print();
        
        new Thread(new Runnable() {
            public void run() {
                for(int i=0;i<10;i++) {
                    business.print_A();
                }
            }
        }).start();
        
        new Thread(new Runnable() {
            public void run() {
                for(int i=0;i<10;i++) {
                    business.print_B();
                }
            }
        }).start();
        
    }
}
class Print {
    
    private boolean flag = true;
    
    public synchronized void print_A () {
        while(!flag) {
            try {
                this.wait();
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
        System.out.print("A");
        flag = false;
        this.notify();
    }
    
    public synchronized void print_B () {
        while(flag) {
            try {
                this.wait();
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
        System.out.print("B");
        flag = true;
        this.notify();
    }
}

 

由上面的例子我們可以設計出3個線程乃至於n個線程的程序，下面給出的例子是3個線程，分別打印A，B，C 10次，使之出現ABCABC.. 的效果

 

public class ThreadABC {

    /**
     * @param args
     */
    public static void main(String[] args) {
        
        final Print business = new Print();
        
        new Thread(new Runnable() {
            public void run() {
                for(int i=0;i<100;i++) {
                    business.print_A();
                }
            }
        }).start();
        
        new Thread(new Runnable() {
            public void run() {
                for(int i=0;i<100;i++) {
                    business.print_B();
                }
            }
        }).start();
        
        new Thread(new Runnable() {
            public void run() {
                for(int i=0;i<100;i++) {
                    business.print_C();
                }
            }
        }).start();
        
    }
}
class Print {
    
    private boolean should_a = true;
    private boolean should_b = false;
    private boolean should_c = false;
    
    public synchronized void print_A () {
        while(should_b || should_c) {
            try {
                this.wait();
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
        System.out.print("A");
        should_a = false;
        should_b = true;
        should_c = false;
        this.notifyAll();
    }
    
    public synchronized void print_B () {
        while(should_a || should_c) {
            try {
                this.wait();
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
        System.out.print("B");
        should_a = false;
        should_b = false;
        should_c = true;
        this.notifyAll();
    }
    
    public synchronized void print_C () {
        while(should_a || should_b) {
            try {
                this.wait();
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
        System.out.print("C");
        should_a = true;
        should_b = false;
        should_c = false;
        this.notifyAll();
    }
}

 

再一次證明了軟件工程的重要性了；在多線程程序中，應該說在程序中，我們應該把那些業務邏輯代碼放到同一個類中，使之高內聚，低耦合