Please read the question

Please write down what this code outputs?

/**
 * @author 面試專(zhuān)欄
 * @date 2021/7/11 13:57
 */
public class Test1 {
    public static void main(String[] args) {
        //輸出什么？
        test();
    }

    public static void test() {
        for (int i = 4; i > 0; i--) {
            int j = 0;
            do {
                j++;
                if (j == 2) {
                    break;
                }
            } while (j <= i);
            System.out.print(j);
        }
    }
}

Seeing this question, many people will think it is too simple. In fact, this question examines three knowledge points;

• forloop
• do...whileLoop
• breakExit

Don’t underestimate me, too I have asked many people, and the answers are all strange. Four answers appear most frequently:

• 第一個(gè)：4321
• 第二個(gè)：1232
• 第三個(gè)：2211
• 第四個(gè)：2222

你覺(jué)得是哪個(gè)？還是覺(jué)得都不是？

注意點(diǎn)

注意點(diǎn)1

do...while循環(huán)是while循環(huán)的變種，在檢查條件是否為真之前，該循環(huán)其實(shí)已經(jīng)執(zhí)行過(guò)一次了，然后在檢查條件是否為真，如果為true，就重復(fù)執(zhí)行這個(gè)循環(huán)。注意：只要循環(huán)體中執(zhí)行break后也會(huì)結(jié)束循環(huán)。

注意點(diǎn)2

for(表達(dá)式1；表達(dá)式2；表達(dá)式3){
//循環(huán)體
}

這個(gè)循環(huán)體執(zhí)行步驟如下：

• The first step: execute initialization: expression 1 (will only be executed once)
• The second step: execute expression 2, if expression 2 If the result is false, the loop ends, otherwise the loop body is executed, and then expression 3 is executed.
• Step 3: Loop step 2, when the result of expression 2 is false , exit the loop, or encounter the return, break keywords.

Ontology analysis

• ##When entering the for loop body for the first time, i=4, and then included in the do...while loop body. At this time, j=0, and then this loop continues to execute j until j=2 or j>i exits the loop body. Obviously, j=2 at this time, also That is, the output at this time is 2.

• The next time the for loop, i=3, the output is still 2,

• The next for loop, i=2, the same output is still 2,

• The next for loop, i=1, the same output The result is 2. At this time, the i-- operation of the foe loop is executed, i=0, and the condition of i>0 is not met. At this time, the for loop exits.

2222.

Postscript