方法内的变量为线程安全

Java栈：线程私有，用于存放局部变量，方法参数，同时和java方法的调用返回密切相关。

栈上分配的基本思想，是将线程私有的对象，打散分配到栈上，分配在栈上的函数调用结束后对象会自行销毁，不需要垃圾回收接入:方法内部变量线程安全

public class Text {    public static void main(String[] args) throws InterruptedException {        // TODO Auto-generated method stub        HasSelfPrivateNum num = new HasSelfPrivateNum();        ThreadA a = new ThreadA(num);        ThreadB b = new ThreadB(num);        a.start();        b.start();    }}public class HasSelfPrivateNum {    public void addI(String username) {        int num;        if (username.equals("a")) {            num = 100;            System.out.println("a set over");            try {                Thread.sleep(2000);            } catch (InterruptedException e) {                // TODO Auto-generated catch block                e.printStackTrace();            }        } else {            num = 200;            System.out.println("b set over");        }        System.out.println(username + "num = " + num);    }}public class ThreadA extends Thread {    public HasSelfPrivateNum num;    public ThreadA(HasSelfPrivateNum num) {        // TODO Auto-generated constructor stub        this.num = num;    }    public void run() {        // TODO Auto-generated method stub        num.addI("a");    }}public class ThreadB extends Thread{    private HasSelfPrivateNum num;    public ThreadB(HasSelfPrivateNum num) {        // TODO Auto-generated constructor stub        this.num = num;    }    public void run() {        // TODO Auto-generated method stub        num.addI("b");    }}