while 迴圈

Java 中級

Jim White

Java Developer

while 迴圈如何運作

先檢查條件
- 若為 true，執行區塊程式碼
- 否則，迴圈結束
重複：先檢查條件再決定

while 迴圈示意圖

while 迴圈語法

while (condition) {

  // Run this code

}

語法類似 if 陳述式
與 if 不同，可重複執行多次

while 迴圈範例

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

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

無限 while 迴圈

忘記更新變數

int counter = 1;

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

➡ 造成程式卡住

條件永遠為 true

int counter = 1;

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

更新運算子

int counter = 0;

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

類似： -=, *=, /=, ...

break

可用 break 提早離開 while 迴圈，但不算佳式

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

重點回顧

// 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;
  }
}

一起來練習吧！

Java 中級