Ele.me's written test questions seem simple, but it stumps a lot of people

Please read the question

Please write down what this code outputs?

/** * @author 面试专栏 * @date 2021/7/11 13:57 */ public class Test1 { public static void main(String[] args) { //输出什么？ 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:

• 第一个： 4321
• 第二个： 1232
• 第三个： 2211
• 第四个： 2222

你觉得是哪个？还是觉得都不是？

注意点

注意点1

do...while循环是while循环的变种，在检查条件是否为真之前，该循环其实已经执行过一次了，然后在检查条件是否为真，如果为true，就重复执行这个循环。注意：只要循环体中执行break后也会结束循环。

注意点2

for(表达式1；表达式2；表达式3){ //循环体 }

这个循环体执行步骤如下：

• 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, breakkeywords.

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