设计4个线程，其中两个线程每次对j增加1，另外两个线程对j每次减少1。写出程序

以下程序使用内部类实现线程，对j增减的时候没有考虑顺序问题。
public class ThreadTest1 {
private int j;

public static void main(String args[]) {
ThreadTest1 tt = new ThreadTest1();
Inc inc = tt.new Inc();
Dec dec = tt.new Dec();
for (inti = 0; i < 2; i++) {
Thread t = new Thread(inc);
t.start();
t = new Thread(dec);
t.start();
}
}

private synchronized void inc() {
j++;
System.out.println(Thread.currentThread().getName() + "-inc:" + j);
}

private synchronized void dec() {
j--;
System.out.println(Thread.currentThread().getName()+"-dec:"+j);
}

class Inc implements Runnable {
public void run() {
for (inti = 0; i < 100; i++) {
inc();
}
}
}

class Dec implements Runnable {
public void run() {
for (inti = 0; i < 100; i++) {
dec();
}
}
}
}

----------随手再写的一个-------------
class A {
JManger j = new JManager();

public static void main(String[] args) {
new A().call();
}

void call() {
for (int i = 0; i < 2; i++) {
new Thread(new Runnable() {
public void run() {
while (true) {
j.accumulate();
}
}
}).start();
new Thread(new Runnable() {
public void run() {
while (true) {
j.sub();
}
}
}).start();
}
}
}

class JManager {
private int j = 0;

public synchronized void subtract()
{
j--
}

public synchronized void accumulate() {
j++;
}
}