while 循环

Java 中级

Jim White

Java Developer

while 循环原理

先检查条件
- 若为 true，则运行给定代码
- 否则，循环结束
重复：再次检查条件，然后决定

while 循环示意图

while 语法

while (condition) {

  // Run this code

}

语法与 if 语句相似
不同于 if，可多次运行

while 示例

// Prints numbers smaller than 5
int counter = 1;

while (counter < 5){
  System.out.println(counter);
  counter = counter + 1;
}

无限 while 循环

忘记更新变量

int counter = 1;

while (counter < 5){
  System.out.println(counter);
  counter = counter + 0;
}

➡ 程序挂起

条件始终为 true

int counter = 1;

while (counter < 5){
  System.out.println(counter);
  counter = counter - 1;
}

更新运算符

int counter = 0;

// Same as counter = counter + 3
counter += 3;

类似于 -=, *=, /=, ...

break

可用 break 提前退出 while 循环，但并非最佳实践

int counter = 1;
while (counter < 5){
    System.out.println("Counter: " + counter);
    if (counter == 3) {
        break; // Exit the loop when counter is 3
    }
    counter+=2;
}

Counter: 1
Counter: 3

回顾

// while loop that prints even numbers smaller than 20
int counter = 2;

while (counter < 20){
  System.out.println(counter);
  counter *= 2;

  // Exit while loop if counter is odd
  if (counter % 2 == 1){ // counter % 2 is counter modulo 2
    System.out.println("Something went wrong, counter is odd.");
    break;
  }
}

Passons à la pratique !

Java 中级