while() 和 if()else() 和 switch()case()break

whlie和if...else 和 switch()case()break

if...else

package com.scanner;

import java.util.Scanner;
                                          //if判断
public class Demo01 {
    public static void main(String[] args) {
        int i = 0;
        float f = 0.0f;
        System.out.println("请输入整数：");

        Scanner A = new Scanner(System.in);
        if (A.hasNextInt()) {
            i = A.nextInt();
            System.out.println("整数为：" + i);
        } else {
            A.next();
            System.out.println("输入不是整数");

        }


        System.out.println("请输入小数：");


        if (A.hasNextFloat()) {
            f = A.nextFloat();
            System.out.println("小数为：" + f);
        } else {
            System.out.println("输入不是小数");

        }
        A.close();
    }
}

while

package com.scanner;

import java.util.Scanner;

                                       //whlie
                                       // 输入数字，非数字结束，求和，平均数
public class Demo03 {
    public static void main(String[] args) {
        double sum = 0;
        int x = 0;

        System.out.println("请输入数据，非数字结束");
        Scanner scanner = new Scanner(System.in);
        while (scanner.hasNextDouble()) {
                                            //当while()为ture,{}会一直循环
            double y = scanner.nextDouble();
            sum = sum + y;
            x = x + 1;
            System.out.println("和为：" + sum + " ,共" + x + "数");

        }
        System.out.println("和为：" + sum);
        System.out.println("平均为：" + (sum / x));


                                                //do()while()至少走一次
        int i = 0;
        int Sum = 0;
        do {
            Sum = Sum + i;
            i++;
        }
        while (i <= 100);
        System.out.println(Sum);
    }
}

switche()case()break

                        //switch   case   break
public class SwitchCsaeBreak {
        public static void main(String[] args) {
        String name="小哥";
//JDK7的新特性,表达式结果可以是字符串! ! !
// 字符的本质还是数字
//反编译java---class (字节码文件)----反编译(IDEA)
switch (name){
            case"小姐姐":
                System.out.println("小姐姐");
                break;
            case "小哥":
                System.out.println("小哥哥");
                break;
            default:
                System.out.println("弄啥呦!");
        }
    }