动手动脑及课后实验性问题

P37 Enumtest.java

package com.ith;

public class EnumTest {

    public static void main(String[] args) {
        Size s=Size.SMALL;
        Size t=Size.LARGE;
        //s和t引用同一个对象？
        System.out.println(s==t);  //
        //是原始数据类型吗？
        System.out.println(s.getClass().isPrimitive());
        //从字符串中转换
        Size u=Size.valueOf("SMALL");
        System.out.println(s==u);  //true
        //列出它的所有值
        for(Size value:Size.values()){
            System.out.println(value);
        }
    }

}
enum Size{SMALL,MEDIUM,LARGE};

 

P52

package com.ith;

import java.util.*;

public class InputTest
{
    public static void main(String[] args)
    {
        Scanner in = new Scanner(System.in);

        // get first input
        System.out.print("What is your name? ");
        String name = in.nextLine();

        // get second input
        System.out.print("How old are you? ");
        int age = in.nextInt();


    /* int i;
     String value="100";
     i=Integer.parseInt(value);
     i=200;
     String s=String.valueOf(i);*/

        // display output on console
        System.out.println("Hello, " + name + ". Next year, you'll be " + (age + 1));


    }
}

 P56

package com.ith;



public class TestDouble {

    public static void main(String args[]) {
        System.out.println("0.05 + 0.01 = " + (0.05 + 0.01));
        System.out.println("1.0 - 0.42 = " + (1.0 - 0.42));
        System.out.println("4.015 * 100 = " + (4.015 * 100));
        System.out.println("123.3 / 100 = " + (123.3 / 100));
    }
}

P59

package com.ith;




import java.math.BigDecimal;

public class TestBigDecimal
{
    public static void main(String[] args)
    {
        BigDecimal f1 = new BigDecimal("0.05");
        BigDecimal f2 = BigDecimal.valueOf(0.01);
        BigDecimal f3 = new BigDecimal(0.05);
        System.out.println("下面使用String作为BigDecimal构造器参数的计算结果：");
        System.out.println("0.05 + 0.01 = " + f1.add(f2));
        System.out.println("0.05 - 0.01 = " + f1.subtract(f2));
        System.out.println("0.05 * 0.01 = " + f1.multiply(f2));
        System.out.println("0.05 / 0.01 = " + f1.divide(f2));
        System.out.println("下面使用double作为BigDecimal构造器参数的计算结果：");
        System.out.println("0.05 + 0.01 = " + f3.add(f2));
        System.out.println("0.05 - 0.01 = " + f3.subtract(f2));
        System.out.println("0.05 * 0.01 = " + f3.multiply(f2));
        System.out.println("0.05 / 0.01 = " + f3.divide(f2));
    }
}

 

P62

import java.math.BigDecimal;

public class TestBigDecimal

{

public static void main(String[] args)

{

int x=100;

int y=200;

System.out.println("x+y="+x+y);

System.out.println(x+y+"=x+y");

}

}

 

四则运算

package com.ith;

//信2205-1  20223974 李文静

import java.util.Random;

public class y {


    public static void main(String[] args) {

        for(int i=0;i<30;i++){
            Random rand = new Random();
            int firstnum = rand.nextInt(100);
            int secondnum = rand.nextInt(100);
            int num = rand.nextInt(4);
            if(num==1)
                System.out.println(firstnum+" + "+secondnum+" = ");
            if(num==2)
                System.out.println(firstnum+" - "+secondnum+" = ");
            if(num==3)
                System.out.println(firstnum+" * "+secondnum+" = ");
            if(num==4)
                System.out.println(firstnum+" / "+secondnum+" = ");
        }
    }
}