[每日一练] Java多线程

Java控制台程序 modified at 2014年4月15日8:54:55

题目1：有100个线程，每个线程对变量 j 加 1，所有线程结束后，输出 j 的值（结果为100）。

提示：

1）对 j 的修改函数或者变量 j 进行同步（synchronized）处理。

2）所有线程都放入ThreadGroup线程组，threadGroup.activeCount>0检测所有线程是否完结。

难度：中

题目2：在题目1的基础上，利用这100个线程，每个线程对变量 j 减 1 ，所有线程结束后，输出 j 的值（结果为0）。

难度：中

public class AccountThread {

Account account = new Account(0);
Thread[] thread = new Thread[100];
/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
AccountThread at = new AccountThread();
}
public AccountThread(){
ThreadGroup g = new ThreadGroup("thread group");

System.out.println("Thread\tOperate\t\tBalance");

for(int i=0;i<100;i++){
thread[i] = new Thread(g,new MyThread(1),"thread"+i);
thread[i].start();
}

while(g.activeCount()!=0){	}
System.out.println("after deposit:\t\t"+this.account.getBalance());

for(int i=0;i<100;i++){
thread[i] = new Thread(g,new MyThread(-1),"thread"+i);
thread[i].start();
}

while(g.activeCount()!=0){	}
System.out.println("after withdraw:\t\t"+this.account.getBalance());
}
class MyThread extends Thread{
int amount = 0;
public MyThread(int a){
amount = a;
}
@Override
public void run(){
account.deposit(amount);
}
}
class Account{
int _balance;
public Account(int balance){
_balance = balance;
}
public int getBalance(){
return _balance;
}
public void deposit(int amount){
synchronized((Object)_balance){
_balance += amount;
System.out.println(Thread.currentThread().getName() +
" deposit " + amount+"\t\t"+getBalance());
try {
Thread.sleep(100);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}
}

题目3：有一个账号，初始余额为 0 ，有两个线程，

1）线程1对账号存入随机钱，线程2从账号取出随机钱，

2）当账号余额不足时，线程2等待线程1存钱，

3）每一次存钱、取钱操作输出余额或者余额不足信息。

提示：需要用到资源的同步（synchronized）、线程的等待（wait）和通知（notify）。

难度：难

package com.threadexercise;

public class AccountThread {
Account account = new Account(100);
boolean done = false;
boolean over = false;
/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
AccountThread at = new AccountThread();
System.out.println("Thread1\t\tThread2\t\tBalance");
}
public AccountThread(){
ThreadGroup g = new ThreadGroup("group");
DepositThread dt = new DepositThread();
dt.start();
WithdrawThread wt = new WithdrawThread();
wt.start();
}
class DepositThread extends Thread{
@Override
public void run(){
while(true){
int n = (int)(Math.random()*10)+1;
account.deposit(n);
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}
class WithdrawThread extends Thread{
@Override
public void run(){
while(true){
int n = (int)(Math.random()*10)+1;
account.withdraw(n);
try {
Thread.sleep(10);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}
class Account{
public Account(int amount){
balance = amount;
}
int balance;
public int getBalance(){
return balance;
}
public synchronized void deposit(int amount){
balance+=amount;
System.out.println("deposit: "+amount+"\t\t\t\t"+account.getBalance());
notifyAll();
}
public synchronized void withdraw(int amount){
while(balance < amount){
System.out.println(balance +" < " + amount + " not enough");

try {
wait();
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}

}
balance -= amount;
System.out.println("\t\twithdraw: "+amount+"\t\t"+account.getBalance());
}
}
}

题目4：有四个线程，其中两个对变量 j 加一，另外两个对变量 j 减一。

难度：中

package com.ThreadExercise;

public class SimpleThread {

/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
System.out.println("Thread\t\tamount\t\tJ");
SimpleThread st = new SimpleThread();
}
public SimpleThread(){
int number;
for(int i=0;i<2;i++){
number = (int)(Math.random())+1;
Thread t1 = new Thread(new MyThread(1));
t1.setName("Thread"+i);
t1.start();
}
for(int i=0;i<2;i++){
number = (int)(Math.random())+1;
Thread t1 = new Thread(new MyThread(-1));
t1.setName("Thread"+(i+2));
t1.start();
}
//number = (int)(Math.random()*10)+1;
Thread control = new Thread(new Thread(new ControlThread(30000)));
control.start();
}
int j = 0;
boolean mark = true;
public synchronized void operateJ(int amount){
j += amount;
System.out.println(Thread.currentThread().getName()+"\t\t"+amount+"\t\t"+j);
}
class ControlThread implements Runnable{
int time;
public ControlThread(int amount){
this.time = amount;
}
@Override
public void run(){
try {
System.out.println("after "+time+" seconds stop!");
Thread.sleep(time);
mark = false;
System.out.println("threads stopped!");
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
class MyThread implements Runnable{
int amount;
public MyThread(int num){
amount = num;
}
@Override
public void run(){
while(mark){
operateJ(amount);
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}
}

题目5：用Runnable接口和Thread基类分别

1）实现一个线程，能够传递参数

2）定义线程名称，在控制台输出名称和参数

3）放入ThreadGroup，当两个线程结束后，输出提示信息

难度：易

题目6：用Java语言描述出Thread的生命周期。

提示：创建、启动、运行、阻塞（时间片、wait、中断）

难度：易

PS：该类练习题，保证线程正确，并发的效率难以保证。