多線程（一、線程安全案例）

案例：

假設(shè)有四個人，頻繁地通過海關(guān)出口，規(guī)定每次只能通過一個人，通過一個人時，將通過海關(guān)的總?cè)舜渭?，同時記錄該次通過人的姓名和出生地，如果出生地和名字不一致，不允許通過。

海關(guān)代碼

package com.jane.service;

/**
 * 海關(guān)入口
 */
public class GateWay {
    private int counter = 0;
    private String name = "無名";
    private String address = "無地址";
# 
    /**
     * 通行
     * @param name
     * @param address
     */
    public void pass(String name, String address) {
        this.counter++;
        this.name = name;
        this.address = address;
        checkPassport();
    }

    /**
     * 檢查護(hù)照
     */
    private void checkPassport() {
        //名字和地址匹配上才能通過
        if(!this.name.equals(this.address)) {
            System.out.println("禁止通行:" + "第" + this.counter + "人，姓名：" + this.name + ",來自：" + this.address);
        }
    }

}

人的代碼

package com.jane.service;

/**
 * 人模擬線程，循環(huán)入關(guān)
 */
public class Person extends Thread{
   private final GateWay gateWay;
   private final String name;
   private final String address;

   public Person(GateWay gateWay, String name, String address) {
       this.gateWay = gateWay;
       this.name = name;
       this.address = address;
   }

   public void run() {
       System.out.println(this.name + "，開始入關(guān)");
       while(true) {
          this.gateWay.pass(this.name, this.address);
       }
   }
}

啟動函數(shù)

System.out.println("開始入關(guān)");
        GateWay gate = new GateWay();
        new Person(gate, "張三", "張三").start();
        new Person(gate, "李四", "李四").start();
        new Person(gate, "王五", "王五").start();
        new Person(gate, "趙六", "趙六").start();

運行結(jié)果

線程不安全?。。。。。。。。。。?！

優(yōu)化后（synchronized），線程安全