public class TextSync implements Runnable{
  /**未处理线程同步
   * @param args
   */
  Time time = new Time();
  public static void main(String[] args) {
    TextSync text = new TextSync();
    Thread t1 = new Thread(text);
    Thread t2 = new Thread(text);
    t1.setName("t1");
    t2.setName("t2");
    t1.start();
    t2.start();
  }
  @Override
  public void run() {
    time.add(Thread.currentThread().getName());
  }
}
class Time {
  private static int num = 0;
  public void add(String name){
    try {
      num++;
      //当第一个线程执行到此时，num变成了1，第一个线程暂停一秒，
      //第二个线程开始执行，当第二个线程执行到此时，num变成了2，第二个线程暂停一秒，
      //第一个线程此时的num同样变成了2，所以最终的结果均为2；
      Thread.sleep(1000);
    } catch (InterruptedException e) {
      e.printStackTrace();
    }
    System.out.println(name+"是第"+num+"个执行的线程。");
  }
}

t2是第2个执行的线程。
t1是第2个执行的线程。

public class TextSynctwo implements Runnable{
  /**线程同步
   * @param args
   */
  Time1 time = new Time1();
  public static void main(String[] args) {
    TextSynctwo text = new TextSynctwo();
    Thread t1 = new Thread(text);
    Thread t2 = new Thread(text);
    t1.setName("t1");
    t2.setName("t2");
    t1.start();
    t2.start();
  }
  @Override
  public void run() {
    time.add(Thread.currentThread().getName());
  }
}
class Time1 {
  private static int num = 0;
  
  //synchronized锁定当前线程，可以在方法定义时进行声明，或采用在方法中进行设置。
  public synchronized void add(String name){
    //synchronized (this) {//锁定当前线程，防止此时被别的线程执行
      try {
        num++;
        Thread.sleep(1000);
      } catch (InterruptedException e) {
        e.printStackTrace();
      }
      System.out.println(name+"是第"+num+"个执行的线程。");
    //}
  }
}

t1是第1个执行的线程。
t2是第2个执行的线程。

public class TestDeadLock implements Runnable{
  /**死锁
   * @param args
   */
  private int flag = 0 ; 
  static Object o1 = new Object();
  static Object o2 = new Object();
  public static void main(String[] args) {
    TestDeadLock td1 = new TestDeadLock(); 
    TestDeadLock td2 = new TestDeadLock(); 
    td1.flag = 1;
    td2.flag = 2;
    Thread t1 = new Thread(td1); 
    Thread t2 = new Thread(td2);
    t1.setName("t1");
    t2.setName("t2");
    t1.start();
    t2.start();
  }

  @Override
  public void run() {
    System.out.println(Thread.currentThread().getName());
    if(flag == 1){
      synchronized(o1){
        try {
          Thread.sleep(5000);
        } catch (InterruptedException e) {
          e.printStackTrace();
        }
        synchronized(o2){
          System.out.println("1");
        }
      }
    }
    if(flag == 2){
      synchronized(o2){
        try {
          Thread.sleep(5000);
        } catch (InterruptedException e) {
          e.printStackTrace();
        }
        synchronized(o1){
          System.out.println("2");
        }
      }
    }
  }
}

public class TT implements Runnable{
  /**锁定
   * @param args
   */
  int b = 100;
  public static void main(String[] args) {
    TT tt = new TT();
    Thread th = new Thread(tt);
    th.start();
    try {
      tt.m2();
    } catch (Exception e) {
      e.printStackTrace();
    }
    System.out.println(tt.b);
  }
  @Override
  public void run() {
    try {
      m1();
    } catch (Exception e) {
      e.printStackTrace();
    }
  }
  private synchronized void m1() throws Exception{
    b = 1000;
    Thread.sleep(5000);
    System.out.println("b="+b);
  }
  private synchronized void m2() throws Exception{
    Thread.sleep(2500);
    b = 2500;
  } 
}

1000
b=1000