Java学习day05

顺序、选择、循环结构

package com.Hape.Structure;

import java.util.Scanner;

public class IfDemo01 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入内容：");
        String str = scanner.nextLine();

        if(str.equals("Hello")){
            System.out.println("Hello");
        }
        System.out.println("END");

        scanner.close();
    }

}

package com.Hape.Structure;

public class WhileDemo01 {
    public static void main(String[] args) {
        //输出1—100
        int i = 0;
        int j = 0;

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

package com.Hape.Structure;

public class DoWhileDemo01 {
    public static void main(String[] args) {

        int i = 0 ;
        int sum = 0 ;

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

        //while和Do-While的区别：While先判断后执行，Do-While先执行后判断
    }
}

package com.Hape.Structure;

import java.util.Scanner;

public class SwitchDemo01 {
    public static void main(String[] args) {

        Scanner scanner = new Scanner(System.in);

        System.out.println("请输入成绩：");
        String grade = scanner.nextLine();


        switch (grade){
            case "A":
                    System.out.println("优秀");
                    break;//可选
            case "B":
                System.out.println("良");
                break;//可选
            case "C":
                System.out.println("及格");
                break;//可选
            case "D":
                System.out.println("再接再厉");
                break;//可选
            case "E":
                System.out.println("挂科");
                break;//可选
            default:
                System.out.println("未知等级");

                scanner.close();


            //case穿透  //switch 匹配一个合适的值
            //不加break：程序一直执行，
            //break尽量加上

        }
    }
}

package com.Hape.Structure;

import java.util.Scanner;

public class IfDemo01 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入内容：");
        String str = scanner.nextLine();

        if(str.equals("Hello")){
            System.out.println("Hello");
        }
        System.out.println("END");

        scanner.close();
    }

}

package com.Hape.Structure;

public class ForDemo01 {
    public static void main(String[] args) {
        /*
        for(初始化;布尔表达式;更新){

        代码语句

        }
         */

        // 初始化  //判断   //迭代
        for(int i=1;i<=100;i++){
            System.out.println(i);

        }
        System.out.println("For循环结束");

        /*
        //死循环
        for(;;){


        }
         */

    }
}

package com.Hape.Structure;

public class ForDemo02 {
    public static void main(String[] args) {

        //计算1~100之间奇数和偶数的和

        int oddsum = 0;
        int evensum = 0;

        for (int i = 0; i <= 100; i++) {
            if(i%2==0){
                evensum+=i;
            }else{
                oddsum+=i;
            }
        }
        System.out.println("奇数的和："+oddsum);
        System.out.println("偶数的和："+evensum);

    }
}

package com.Hape.Structure;

public class ForDemo03 {
    public static void main(String[] args) {
        //输出1~1000之间能被5整除的数字，每行输出3个
        for (int i = 1; i <=1000; i++) {
            if(i%5==0){
                System.out.print(i+"\t");
            }
            if (i%(5*3)==0){
                System.out.println();
                //System.out.print("\n");
            }

        }
    }
}
//System.out.println(); 输出完自动换行
//System.out.print(); 输出完不会换行

package com.Hape.Structure;

public class ForDemo04 {
    public static void main(String[] args) {

        //打印九九乘法表


        for (int j = 1; j < 10; j++) {

            for (int i = 1; i <= j; i++) {

                System.out.print(i+"x"+j+"="+j*i+"\t");
            }

            System.out.println();
            }

        }
    }

package com.Hape.Structure;

public class ForceForDemo01 {
    public static void main(String[] args) {
        int[] numbers = {10,20,30,40,50};

        for(int x:numbers){
            System.out.println(x);
        }
    }
}

public class BreakContinueDemo01 {
    public static void main(String[] args) {
        //break--强行退出循环
        //continue--终止某次循环

        int i = 0;
        while(i<=100){
            i++;
            if(i==30){
                break;
            }
            System.out.println(i);
        }

        System.out.println("===================================");
        int m = 0;
        while(m<=100){
            m++;
            if(m%10==0){
                System.out.println();
                continue;//碰到10的倍数，直接跳到循环开头
            }

            System.out.print(m);
        }
    }
}

package com.Hape.Structure;

public class TestDemo01 {

    //打印三角形 5行三角形
    public static void main(String[] args) {

        for (int i = 1; i <= 5; i++) {
            for (int j = 5; j >= i; j--) {
                System.out.print(" ");
            }
            for (int j = 1; j <= i; j++) {
                System.out.print("#");
            }
            for (int j = 1; j<i;j++){
                System.out.print("#");
            }
            System.out.println();

            }


        }
    }