面试题

一、银行一个账户，同时有两个人分别向该账户存 3000 元，每次存 1000，存 3 次，每次存完打印用户余额

package com.test3;

public class Test1 {
    public static void main(String[] args) {
        Account act = new Account();
        Customer c1 = new Customer(act );
        Customer c2 = new Customer(act );
        
        c1.setName("账户1");
        c2.setName("账户2");
        
        c1.start();
        c2.start();
    }
}


class Account{
    double balance;
    public Account() {
        
    }
    
    public synchronized void addMoney(double amt) {
        this.balance += amt;
        try {
            Thread.currentThread().sleep(10);
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        System.out.println(Thread.currentThread().getName()+","+balance);
        
    }
}

class Customer extends Thread{
    Account account;
    
    public Customer(Account act) {
        this.account = act;
    }
    
    @Override
    public void run() {
        for (int i = 0; i < 3; i++) {
            account.addMoney(1000);
        }
    }
}

二、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

package com.test3;

public class Test3 {
    public static void main(String[] args) {
        NumberFactory num = new NumberFactory();
        IncNumber incNumber = new IncNumber(num);
        DescNumber descNumber = new DescNumber(num);
        
        Thread inc1 = new Thread(incNumber);
        Thread inc2 = new Thread(incNumber);
        Thread inc3 = new Thread(descNumber);
        Thread inc4 = new Thread(descNumber);
        
        inc1.setName("线程一");
        inc2.setName("线程二");
        inc3.setName("线程三");
        inc4.setName("线程四");
        
        inc1.start();
        inc2.start();
        inc3.start();
        inc4.start();
        
    }
    
}

class NumberFactory{
    int j;
    public NumberFactory() {
    }
    
    //自加
    public synchronized void inc(int num) {
        j += num;
        
        System.out.println(Thread.currentThread().getName()+","+j);
    }
    
    //自减
    public synchronized void desc(int num) {
        j -= num;
        
        System.out.println(Thread.currentThread().getName()+","+j);
    }
    
}

class IncNumber implements Runnable{
    NumberFactory numberFactory;
    
    public IncNumber(NumberFactory num) {
        numberFactory = num;
    }

    @Override
    public void run() {
        numberFactory.inc(1);
    }
}

class DescNumber implements Runnable{
    NumberFactory numberFactory;
    
    public DescNumber(NumberFactory num) {
        numberFactory = num;
    }

    @Override
    public void run() {
        numberFactory.desc(1);
    }
}

三、使用两个线程打印 1 - 100。线程一和线程二交替打印

public class Test4 {
    public static void main(String[] args) {
        PrintNum p = new PrintNum();
        Thread th1 = new Thread(p);
        Thread th2 = new Thread(p);
        
        th1.setName("线程一");
        th2.setName("线程二");
        
        th1.start();
        th2.start();
    }
}

class PrintNum implements Runnable{

    int i = 1;
    
    @Override
    public void run() {

        while(true) {
            synchronized (this) {
                
                notify();
                
                if (i <= 100) {
                    System.out.println(Thread.currentThread().getName() + ":" + i);
                    i++;
                } else {
                    break;
                }
                
                try {
                    wait();
                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
                
            }
        }
        
    }
    
}