Java循环

Java循环包括while循环、DoWhile循环、For循环。

while循环

while循环当满足条件后才执行循环里面的内容。实例代码如下：

package com.visual.example;

import java.util.Scanner;

public class DoWhileCircle {
  public static void main(String[] args) {
    Scanner in = new Scanner(System.in);
    int number = (int) (Math.random() * 100 + 1);
    //     while循环
        int Counter = 1;
        int guessNumber;
        System.out.print("请输入一个数字：");
        guessNumber = in.nextInt();
        while (guessNumber != number) {
          Counter += 1;
          if (guessNumber > number) {
            System.out.println("猜大了");
            System.out.print("请输入一个数字：");
            guessNumber = in.nextInt();
          } else if (guessNumber < number) {
            System.out.println("猜小了");
            System.out.print("请输入一个数字：");
            guessNumber = in.nextInt();
          } else {
            System.out.println("恭喜你，猜对了！" + "你猜了" + Counter + "次");
          }
        }
        System.out.println("恭喜你，猜对了！" + "你猜了" + Counter + "次");
  }
}

while循环本体部分：

        while (guessNumber != number) {
          Counter += 1;
          if (guessNumber > number) {
            System.out.println("猜大了");
            System.out.print("请输入一个数字：");
            guessNumber = in.nextInt();
          } else if (guessNumber < number) {
            System.out.println("猜小了");
            System.out.print("请输入一个数字：");
            guessNumber = in.nextInt();
          } else {
            System.out.println("恭喜你，猜对了！" + "你猜了" + Counter + "次");
          }
        }

DoWhile循环部分

DoWhile循环与while循环不同，DoWhile循环可以先进行循环，然后在循环体结束时判断循环条件，然后再判断循环是否继续进行。实例代码如下：

package com.visual.example;

import java.util.Scanner;

public class DoWhileCircle {
  public static void main(String[] args) {
    Scanner in = new Scanner(System.in);
    int number = (int) (Math.random() * 100 + 1);
    int Counter = 0;
    int guessNumber;
    do {
      System.out.print("请输入一个数字：");
      guessNumber = in.nextInt();
      Counter += 1;
      if (guessNumber > number) {
        System.out.println("猜大了");
      } else if (guessNumber < number) {
        System.out.println("猜小了");
      } else {
        System.out.println("恭喜你，猜对了！" + "你猜了" + Counter + "次");
      } // 感觉还不错
    } while (guessNumber != number);
  }
}

DoWhileCircle循环本体：

    do {
      System.out.print("请输入一个数字：");
      guessNumber = in.nextInt();
      Counter += 1;
      if (guessNumber > number) {
        System.out.println("猜大了");
      } else if (guessNumber < number) {
        System.out.println("猜小了");
      } else {
        System.out.println("恭喜你，猜对了！" + "你猜了" + Counter + "次");
      } // 感觉还不错
    } while (guessNumber != number);

For循环

For循环的格式如下：

for(i=1;i<=n;i++)

for( ; ; )第一段的内容为变量的初始化，第二段内容为每次进入循环本体的判断条件，第三段为每执行一次循环体后对变量的操作。

package com.newHorizon.nineninetable;

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

    for (int i = 1; i <= 4; i++) {
      for (int j = 1; j <= i; j++) {
        System.out.print(j + " * " + i + " = " + (i * j) + "\t\t");
      }
      System.out.println();
    }
  }
}

switch case多重选择语句用法

存在多个结果判断时，用if else判断则会很臃肿，所以这个时候可以用switch case进行判断处理。switch case语句格式为：

switch (choice)
  {
    case 1:
      break;
    case 2:
      break;
    case 3:
      break;
    case 4:
      break;
      //bad input
      ...
    case n:
      break;
    default:
      break;
  }

对choice赋值，针对choice不同的值选择不同的case分支，从而快速响应不同的命令情况。代码例子如下：

import java.util.Scanner;

public class SwitchCase {
  public static void main(String[] args) {
    Scanner in = new Scanner(System.in);
    System.out.println("请输入对应的数字1-5：");
    int choice = in.nextInt();
    switch (choice) {
      case 1:
        System.out.println("20多岁的自己，丝毫不比15岁的自己强");
        break;
      case 2:
        System.out.println("隐约雷鸣 阴霾天空 但盼风雨来 能留你在此");
        break;
      case 3:
        System.out.println("隐约雷鸣 阴霾天空 即使天无雨 我亦留此地");
        break;
      case 4:
        System.out.println("大龙猫");
        break;
      case 5:
        System.out.println("起风了，唯有努力生存");
        break;
      default:
        break;
    }
  }
}

Java循环和switch case多重选择