本科生java考试练习题目

前言

论文休息时间，帮实验室的师弟师妹做几道java考试题目，预祝师弟师妹考试取得优异成绩

题目

1、创建3个线程，每个线程睡眠一段时间（0-6秒），然后结束

class SleepFun implements Runnable {
    private int sleepTime = 0;

    public SleepFun(int time) {
        this.sleepTime = time * 1000;
    }

    @Override
    public void run() {
        try {
            Thread.sleep(this.sleepTime);
            System.out.println("Hello World!" + this.sleepTime);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}


public class TestThread {
    public static void main(String args[]) {
        SleepFun f1 = new SleepFun(1);
        SleepFun f2 = new SleepFun(3);
        SleepFun f3 = new SleepFun(5);

        Thread t1 = new Thread(f1);
        t1.start();

        Thread t2 = new Thread(f2);
        t2.start();

        Thread t3 = new Thread(f3);
        t3.start();
    }
}

2、编写一个程序，从键盘读入一个实数，然后检查实数是否小于零，是就抛出异常，否则将这个数开平方

import java.util.Scanner;

public class TestException {
    public double sqrtNumber(double num) throws Exception {
        if (num >= 0) {
            return Math.sqrt(num);
        } else {
            throw new Exception("This number is less than zero!");
        }
    }

    public static void main(String[] args) {
        double num;
        Scanner cin = new Scanner(System.in);

        while (cin.hasNext()) {
            num = cin.nextDouble();

            try {
                TestException te = new TestException();
                double res = te.sqrtNumber(num);
                System.out.println(res);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }

        cin.close();
    }
}