最常见的面试机题，涉及四个线程，两个对j加一，两个对j减一。
这个题太常见了，但是要自己独立的默写出来也不是很容易的哦！
代码：

package renrenPratice;public class testSomeThread {/** * @param args */int j = 10;public static void main(String[] args) {// TODO Auto-generated method stubtestSomeThread tt = new testSomeThread();addJ myaddj = tt.new addJ();minusJ myminusj = tt.new minusJ();for (int m = 0; m < 2; m++) {Thread t = new Thread(myaddj);t.start();t = new Thread(myminusj);t.start();}}private synchronized void addj() {// TODO Auto-generated method stubfor (int k = 0; k < 10; k++) {++j;System.out.println("j++  --> now j is " + j);}}private synchronized void minusj() {// TODO Auto-generated method stubfor (int l = 0; l < 10; l++) {--j;System.out.println("j--  -->  now j is " + j);}}class addJ implements Runnable {@Overridepublic void run() {// TODO Auto-generated method stubaddj();}}class minusJ implements Runnable {@Overridepublic void run() {// TODO Auto-generated method stubminusj();}}}

j++  --> now j is 11j++  --> now j is 12j++  --> now j is 13j++  --> now j is 14j++  --> now j is 15j++  --> now j is 16j++  --> now j is 17j++  --> now j is 18j++  --> now j is 19j++  --> now j is 20j--  -->  now j is 19j--  -->  now j is 18j--  -->  now j is 17j--  -->  now j is 16j--  -->  now j is 15j--  -->  now j is 14j--  -->  now j is 13j--  -->  now j is 12j--  -->  now j is 11j--  -->  now j is 10j++  --> now j is 11j++  --> now j is 12j++  --> now j is 13j++  --> now j is 14j++  --> now j is 15j++  --> now j is 16j++  --> now j is 17j++  --> now j is 18j++  --> now j is 19j++  --> now j is 20j--  -->  now j is 19j--  -->  now j is 18j--  -->  now j is 17j--  -->  now j is 16j--  -->  now j is 15j--  -->  now j is 14j--  -->  now j is 13j--  -->  now j is 12j--  -->  now j is 11j--  -->  now j is 10