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java线程面试手写题
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1.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。
public class Question1 {
private int j = 0;
/**
* @param args
*/
public static void main(String[] args) {
Question1 q = new Question1();
Dec dec = q.new Dec();
Inc inc = q.new Inc();
for(int i=0; i<2;i++){
Thread t2 = new Thread(inc);
t2.start();
Thread t1 = new Thread(dec);
t1.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 {
@Override
public void run() {
inc();
}
}
class Dec implements Runnable {
@Override
public void run() {
dec();
}
}
}
2.设计4个线程， 其中3个线程将一个长度为3的数组每项增加1， 第4个线程输出数组3个数的和写出程序。
public class Question2 {
int[] a = new int[3];
/**
* @param args
*/
public static void main(String[] args) {
Question2 q = new Question2();
Inc inc = q.new Inc();
Print p = q.new Print();
for(int i=0; i<3; i++){
Thread t1 = new Thread(inc);
t1.start();
}
Thread t2 = new Thread(p);
t2.start();
}
private synchronized void inc(){
for(int i=0;i<a.length;i++){
a[i] += 1;
}
System.out.println(Thread.currentThread().getName()+"-inc:"+Arrays.toString(a));
}
private synchronized void print(){
int sum = 0;
for(int i=0;i<a.length;i++){
sum += a[i];
}
System.out.println(Thread.currentThread().getName()+"-print:"+Arrays.toString(a)+"和为："+sum);
}
class Inc implements Runnable {
@Override
public void run() {
inc();
}
}
class Print implements Runnable {
@Override
public void run() {
print();
}
}
}
