147 lines
2.4 KiB
Markdown
147 lines
2.4 KiB
Markdown
---
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id: 控制语句
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title: 控制语句
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sidebar_position: 3
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data: 2022年4月26日
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---
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Java 中的控制语句其实和 C 一样，会涉及刀包括 **if-else、while、do-while、for、return、break、switch**。
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## 条件语句
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### if 语句
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```java
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int a = 10;
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if(a > 10){
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return true;
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}
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return false;
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```
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### if...else 语句
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```java
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int a = 10;
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int b = 11;
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if(a >= b){
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System.out.println("a >= b");
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}else{
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System.out.println("a < b");
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}
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```
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### if...else if 多分支语句
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```java
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int x = 40;
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if(x > 60) {
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System.out.println("x的值大于60");
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} else if (x > 30) {
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System.out.println("x的值大于30但小于60");
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} else if (x > 0) {
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System.out.println("x的值大于0但小于30");
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} else {
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System.out.println("x的值小于等于0");
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}
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```
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### switch 多分支语句
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```java
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switch (week) {
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case 1:
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System.out.println("Monday");
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break;
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case 2:
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System.out.println("Tuesday");
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break;
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case 3:
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System.out.println("Wednesday");
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break;
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case 4:
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System.out.println("Thursday");
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break;
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case 5:
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System.out.println("Friday");
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break;
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case 6:
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System.out.println("Saturday");
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break;
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case 7:
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System.out.println("Sunday");
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break;
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default:
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System.out.println("No Else");
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break;
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}
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```
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## 循环语句
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### while 循环语句
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```java
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while（布尔值）{
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表达式
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}
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```
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### do...while 循环语句
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while 与 do...while 循环的唯一区别是 do...while 语句最少执行一次。
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```java
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int b = 10;
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do {
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System.out.println("b== " + b);
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b--;
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} while(b == 1);
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```
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### for 循环语句
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```java
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for（初始化; 布尔表达式; 步进){}
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```
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每次迭代前会测试布尔表达式，如果获得的结果是 false，就会执行 for 语句后面的代码；每次循环结束，会按照步进的值执行下一次循环。
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#### 逗号操作符
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在 for 语句表达式初始化部分，可以使用一系列的逗号分隔的语句；通过逗号操作符，可以在 for 语句内定义多个变量。
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```java
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for(int i = 1; j = i + 10;i < 5;i++, j = j * 2){}
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```
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#### for-each 语句
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for-each 语句是一种更加简介的、方便对数组和集合进行遍历的方法。
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```java
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int array[] = {7, 8, 9};
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for (int arr : array) {
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System.out.println(arr);
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}
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```
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## 跳转语句
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### break 语句
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终止循环
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### continue 语句
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跳出当前循环、执行下次循环。
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### return 语句
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返回语句
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