package com.blackbread.test;import java.util.ArrayList;import java.util.Collections;import java.util.List;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;public class GoodListHelper<E> {    public List<E> list = Collections.synchronizedList(new ArrayList<E>());    public boolean putIfAbsent(E x) throws InterruptedException {        synchronized (list) {            boolean absent = !list.contains(x);            if (absent) {                if (list.contains(x))                    System.out.println(list.contains(x));                list.add(x);            }            return absent;        }    }    public class PrintA extends Thread {        private GoodListHelper<String> goodListHelper;        private String value;        public PrintA(GoodListHelper<String> goodListHelper, String value) {            this.goodListHelper = goodListHelper;            this.value =http://www.mamicode.com/ value;        }        @Override        public void run() {            try {                goodListHelper.putIfAbsent(value);            } catch (InterruptedException e) {                e.printStackTrace();            }        }    }    public class PrintB extends Thread {        private GoodListHelper<String> goodListHelper;        private String value;        public PrintB(GoodListHelper<String> goodListHelper, String value) {            this.goodListHelper = goodListHelper;            this.value =http://www.mamicode.com/ value;        }        @Override        public void run() {            goodListHelper.list.add(value);        }    }    public static void main(String[] args) throws InterruptedException {        final GoodListHelper<String> goodListHelper = new GoodListHelper<String>();        new Thread(new Runnable() {            @Override            public void run() {                ExecutorService executor = Executors.newFixedThreadPool(50);                for (int i = 0; i < 1000; i++) {                    Thread t = goodListHelper.new PrintA(goodListHelper,                            String.valueOf(i));                    executor.execute(t);                }                executor.shutdown();            }        }).start();        new Thread(new Runnable() {            @Override            public void run() {                ExecutorService executor = Executors.newFixedThreadPool(50);                for (int i = 0; i < 1000; i++) {                    Thread t = goodListHelper.new PrintB(goodListHelper,                            String.valueOf(i));                    executor.execute(t);                }                executor.shutdown();            }        }).start();    }}