Java流程控制

Java流程控制

顺序结构

package com.lzoro.struct;

public class ShunXuDemo {
    public static void main(String[] args) {
        System.out.println("1");
        System.out.println("2");
        System.out.println("3");
        System.out.println("4");
        System.out.println("5");
    }
}

if选择结构

package com.lzoro.struct;

import java.util.Scanner;

//if单选则结构
public class IfDemo01 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("输入内容为：");
        String s = scanner.nextLine();
        //equals:判断字符串是否相等
        if (s.equals("hello")){
            System.out.println(s);
        }
        System.out.println("End");

        scanner.close();
    }
}

package com.lzoro.struct;

import java.util.Scanner;

//if双选择结构
public class IfDemo02 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入成绩：");
        int score = scanner.nextInt();
        if(score>=60){
            System.out.println("及格");
        }else {
            System.out.println("不及格");
        }

        scanner.close();
    }
}

package com.lzoro.struct;

import java.util.Scanner;

//if多选择结构
public class IfDemo03 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入成绩：");
        int score = scanner.nextInt();
        if (score>90){
            System.out.println("优秀");
        }else if (score>70 && score<90){
            System.out.println("良好");
        }else if (score>60 && score<70){
            System.out.println("合格");
        }else {
            System.out.println("不合格");
        }
        scanner.close();


        /*嵌套的if结构
        if(){
            if (){

            }
        }          */
    }
}

Switch选择结构

package com.lzoro.struct;

public class SwitchDemo01 {
    public static void main(String[] args) {
        //case 穿透     switch 匹配一个具体的值
        char grade = 'C';
        switch (grade){
            case 'A':
                System.out.println("优秀");
                break;//可选
            case 'B':
                System.out.println("良好");
                break;
            case 'C':
                System.out.println("合格");
                break;
            case 'E':
                System.out.println("不合格");
                break;
            default:
                System.out.println("未知等级");
        }
    }
}

package com.lzoro.struct;

public class SwitchDemo02 {
    public static void main(String[] args) {
        String name = "优秀";
        //JDK7的新特性，表达结果可以是字符串
        //字符串本质还是数字

        //反编译  java---class(字节码文件)---反编译（IDEA）
        switch (name){
            case"合格":
                System.out.println("合格");
                break;
            case "良好":
                System.out.println("良好");
                break;
            case "优秀":
                System.out.println("优秀");
                break;
            default:
                System.out.println("无所传达等级");
        }
    }
}

While循环

package com.lzoro.struct;

public class WhileDemo01 {
    public static void main(String[] args) {
        //输出1~100
        int i =1;
        while (i<100){
            i++;
            System.out.println(i);
        }
    }
}

输出为2~100

package com.lzoro.struct;

public class WhileDemo02 {
    public static void main(String[] args) {
        //死循环
        while (true){

        }
    }
}

死循环

package com.lzoro.struct;

public class WhileDemo03 {
    public static void main(String[] args) {
        //计算1+2+...+100=?
        int i =1;
        int sum =0;
        while (i<=100){
            sum=sum+i;
            i++;
        }
        System.out.println(sum);
    }

}

DoWhile循环

package com.lzoro.struct;

public class DoWhileDemo01 {
    public static void main(String[] args) {
        int i =1;
        int sum =0;
        do {
            sum=sum+i;
            i++;
        }while (i<=100);
        System.out.println(sum);
    }
}

输出：5050

package com.lzoro.struct;

//dowhile至少循环一次
public class DoWhileDemo02 {
    public static void main(String[] args) {
        int a =0;
        while (a<0){
            System.out.println(a);
            a++;
        }
        System.out.println("====================");
        do {
            System.out.println(a);
            a++;
        }while (a<0);
    }
}

For循环

package com.lzoro.struct;

public class ForDemo01 {
    public static void main(String[] args) {
        int a=1;//初始化条件
        while (a<=100){   //条件判断
            System.out.println(a); //循环体
            a++;    //迭代
        }
        System.out.println("while循环结束！");

            //初始化条件 //条件判断  //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 (; ; ) {

        }
    }
}

输出：1~100的while与for循环

package com.lzoro.struct;

public class ForDemo02 {
    public static void main(String[] args) {
        //练习1：计算0~100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){
                oddsum+=i; //oddsum=oddsum+i;
            }else{
                evensum+=i;
            }
        }
        System.out.println("奇数的和："+oddsum);
        System.out.println("偶数的和："+evensum);
    }
}

package com.lzoro.struct;

public class ForDemo03 {
    public static void main(String[] args) {
        //练习2：用while或for循环输出1~1000之间能被5整除的数，并且每行输出三个
        for (int i = 0; i <= 1000; i++) {
            if (i%5==0){
                System.out.print(i+"\t");
            }
            if (i%(5*3)==0){
                System.out.println("\n");
                //或 System.out.println();
            }

        }
        //println 输出完会换行
        //print   输出完不会换行

    }
}

package com.lzoro.struct;

//练习3：九九乘法表
public class ForDemo04 {
    //1.先打出第一列
    //2.把固定的1用一个循环包起来
    //3.去掉重复项a<=i
    //4.调整样式
    public static void main(String[] args) {
        for (int i = 1; i <= 9; i++) {
            for (int a = 1; a <= i; a++) {
                System.out.print(a+"*"+i+"="+(a*i)+"\t");
            }
            System.out.println();
        }
    }
}

package com.lzoro.struct;

public class ForDemo05 {
    public static void main(String[] args) {
        int[] number = {10,20,39,40,50};  //定义一个数组

        for (int i = 0; i < 5; i++) {
            System.out.println(number[i]);
        }
        System.out.println("================");

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

测试--三角

package com.lzoro.struct;

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

        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();
        }
    }
}