java动手动脑-2024.9.28

枚举类

public class EnumTest {

    public static void main(String[] args) {

        Size s=Size.SMALL;

        Size t=Size.LARGE;

        System.out.println(s==t);

        System.out.println(s.getClass().isPrimitive());

        Size u=Size.valueOf("SMALL");

        System.out.println(s==u);  //true

        for(Size value:Size.values()){

            System.out.println(value);

        }

    }

}

enum Size{SMALL,MEDIUM,LARGE};

输出

false
false
true
SMALL
MEDIUM
LARGE

原码，反码，补码

public class a02Test2 {

    public static void main(String[] args) {

        int a = 100;

        int b = -50;

        System.out.println(a >> 1);

        System.out.println(b >> 1);

    }

}

输出

50
-25

package TestCode3;

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));

    }

}

输出

0.05 + 0.01 = 0.060000000000000005
1.0 - 0.42 = 0.5800000000000001
4.015 * 100 = 401.49999999999994
123.3 / 100 = 1.2329999999999999

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));

    }

}

输出

下面使用String作为BigDecimal构造器参数的计算结果：

0.05 + 0.01 = 0.06

0.05 - 0.01 = 0.04

0.05 * 0.01 = 0.0005

0.05 / 0.01 = 5

下面使用double作为BigDecimal构造器参数的计算结果：

0.05 + 0.01 = 0.06000000000000000277555756156289135105907917022705078125

0.05 - 0.01 = 0.04000000000000000277555756156289135105907917022705078125

0.05 * 0.01 = 0.0005000000000000000277555756156289135105907917022705078125

0.05 / 0.01 = 5.000000000000000277555756156289135105907917022705078125

package TestCode3;

public class Test1 {

    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");

    }

}

package TestCode3;

public class Test1 {

    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");

    }

}

输出

X+Y=100200
300=X+Y

字符串拼接-从前往后

生成100以内随机算式

import java.util.Random;

public class randomMath {

    public static void main(String[] args) {

        Random ch = new Random();

        Random r = new Random();

        Character[] chArr = {'+','-','*','/'};

        for (int i = 0; i < 30; i++) {

            int first = r.nextInt(100);

            int second = r.nextInt(99)+1;

            char c = chArr[ch.nextInt(4)];

            System.out.print(first);

            System.out.print(c);

            System.out.println(second + " = ");

        }

    }

}