java结构

 顺序结构：

一句句执行

 选择结构：

if单选择结构：

if(布尔表达式）{

//如果布尔表达式为true，则执行的语句
}

if多选择表达：

package com.mao.struct;

import java.util.Scanner;

public class IfDome03 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        System.out.println("请输入内容：");

        int score = scanner.nextInt();

        if(score==100){
            System.out.println("恭喜满分");
        } else if (score<100&&score>=90) {
            System.out.println("A级");
        }else if (score<90&&score>=80) {
            System.out.println("B级");
        }else if (score<80&&score>=70) {
            System.out.println("C级");
        }else if (score<70&&score>=60) {
            System.out.println("D级");
        }else{
            System.out.println("成绩不合格");
        }

        scanner.close();
    }
}

嵌套的if结构

switch多选择结构

 

package com.mao.struct;

public class SwitchDemo02 {
    public static void main(String[] args) {

        //反编译：java----class(字节码文件)-----反编译（IDEA)
        String name="貓";
        switch (name){
            case "貓":
                System.out.println("貓");
                break;
            case "兔子":
                System.out.println("Tuzi");
                break;
            default:
                System.out.println("mie");
        }
    }

}

循环结构：

while循环：

package com.mao.struct;

public class WhileDemo03 {
    public static void main(String[] args) {

        int i=1;
        int sum=0;
        while(i<=100){
            sum+=i;
            i++;
        }
        System.out.println(sum);
    }
}

do..while循环：至少会执行一次

 

package com.mao.struct;

public class DoWhileDemo01 {
    public static void main(String[] args) {
        int i=0;
        int sum=0;
        do {

            sum=sum+i;
            i++;
        }while (i<=100);
        System.out.println(sum);
    }
}

for循环：

 计算0-100的偶数和奇数的和

package com.mao.struct;

public class ForDemo02 {
    public static void main(String[] args) {
        //计算0-100之间的奇数和偶数的和

        int oddSum=0;
        int evenSum=0;

        for (int i = 0; i < =100; i++) {
            if(i%2!=0){
                oddSum+=i;
            }else {
                evenSum+=i;
            }
           
        }
        System.out.println(oddSum);
        System.out.println(evenSum);
    }
}

 打印九九乘法表

package com.mao.struct;

public class ForDemo04 {
    public static void main(String[] args) {
        int i,j;
        for(i=1;i<=9;i++){
            for(j=1;j<=i;j++){
                System.out.print(j+"*"+i+"="+(i*j)+" ");
                }
            System.out.println();
            }

        }

}

增强for循环

 

package com.mao.struct;

public class ForDemo05 {
    public static void main(String[] args) {
        int[] numbers = {10, 20, 30, 40};//定义一个数组

        //遍历数组的元素
        for (int x : numbers) {
            System.out.println(x);
        }

    }
}

break和continue

 

break:

package com.mao.struct;

public class BreakDemo01 {
    public static void main(String[] args) {
        int i=0;
        while(i<100){
            i++;
            System.out.println(i);
            if(i==30){
                break; 
            }

        }
    }
}

continue:

 

package com.mao.struct;

public class ContinueDemo01 {
    public static void main(String[] args) {
        int i=0;
        while (i<100){
            i++;
            if(i%10==0){
                System.out.println();
                continue;
            }
            System.out.print(i);
        }
    }
}