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);  //truefor(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 = 0.060.05 - 0.01 = 0.040.05 * 0.01 = 0.00050.05 / 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 = 0.060000000000000002775557561562891351059079170227050781250.05 - 0.01 = 0.040000000000000002775557561562891351059079170227050781250.05 * 0.01 = 0.00050000000000000002775557561562891351059079170227050781250.05 / 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 + " = ");}}}