多线程交替输出问题3种常用解法（多线程经典面试题）

女爷i 2022-09-14 00:25 149阅读 0赞

题目：让两个多线程交替输出  
举例：“ABCDEF”和“123456”，  
输出结果为固定“A1B2C3D4E5F6”

1.利用synchronized+wait/notify

package com.mooc.house.user.controller;
    
    /** * @ClassName sync_wait_notify * @Description DOTO * @Author mischen * @Date 2021/9/30 0030 6:11 * @Version 1.0 **/
    public class sync_wait_notify { 
    
        public static void main(String[] args) { 
            final Object o = new Object();
    
            char[] aI = "ABCDEF".toCharArray();
            char[] aC = "123456".toCharArray();
    
    
            new Thread(()->{ 
                synchronized (o) { 
                    for(char c : aI) { 
                        System.out.print(c);
                        try { 
                            o.notify();
                            o.wait(); //让出锁
                        } catch (InterruptedException e) { 
                            e.printStackTrace();
                        }
                    }
                    o.notify(); //必须，否则无法停止程序
                }
    
            }, "t1").start();
    
            new Thread(()->{ 
                synchronized (o) { 
                    for(char c : aC) { 
                        System.out.print(c);
                        try { 
                            o.notify();
                            o.wait();
                        } catch (InterruptedException e) { 
                            e.printStackTrace();
                        }
                    }
                    o.notify();
                }
            }, "t2").start();
        }
    }

2.利用condition和ReentrantLock联合使用

package com.mooc.house.user.controller;
    
    import java.util.concurrent.locks.Condition;
    import java.util.concurrent.locks.ReentrantLock;
    
    /** * @ClassName T01_00_Question * @Description DOTO * @Author mischen * @Date 2021/9/30 0030 6:17 * @Version 1.0 **/
    public class T01_00_Question { 
    
        private char[] a1 = { '1','2','3','4','5','6'};
        private char[] a2 = { 'A','B','C','D','E','F'};
        private ReentrantLock lock = new ReentrantLock();
        private Condition c1 = lock.newCondition();
        private Condition c2 = lock.newCondition();
    
        public void m1(){ 
            int count = 0;
            lock.lock();
            //这里模拟前面四个数
            while(count <= 5){ 
                System.out.print(a2[count++]);
                try { 
                    c2.signal();
                    c1.await();
                } catch (InterruptedException e) { 
                    e.printStackTrace();
                }
            }
            c2.signal();
            lock.unlock();
        }
    
        public void m2(){ 
            int count = 0;
            lock.lock();
            while(count <= 5){ 
                System.out.print(a1[count++]);
                try { 
                    c1.signal();
                    c2.await();
                } catch (InterruptedException e) { 
                    e.printStackTrace();
                }
            }
            c1.signal();
            lock.unlock();
        }
        public static void main(String[] args) { 
            //要求用线程顺序打印A1B2C3....Z26
            T01_00_Question t = new T01_00_Question();
            new Thread(()->{ 
                t.m1();
            }).start();
            new Thread(()->{ 
                t.m2();
            }).start();
        }
    }

3.利用LockSupport

package com.mooc.house.user.controller;
    
    import java.util.concurrent.locks.LockSupport;
    
    /** * @ClassName Test1 * @Description DOTO * @Author mischen * @Date 2021/9/30 0030 5:42 * @Version 1.0 **/
    public class Test1 { 
    
        static Thread t1 = null,t2=null;
    
        public static void main(String[] args) { 
            char[] a1= "ABCDEF".toCharArray();
            char[] c1= "123456".toCharArray();
    
            t1 = new Thread(() -> { 
                for(char c : a1) { 
                    System.out.print(c);
                    LockSupport.unpark(t2); //叫醒T2
                    LockSupport.park(); //T1阻塞
                }
            }, "t1");
    
            t2 = new Thread(() -> { 
                for(char c : c1) { 
                    LockSupport.park(); //t2阻塞
                    System.out.print(c);
                    LockSupport.unpark(t1); //叫醒t1
                }
            }, "t2");
    
            t1.start();
            t2.start();
        }
    }