【面试二：在JAVA中如何跳出当前的多重嵌套循环】

跳出多重嵌套

目前java主要有for循环、while循环、switch循环、forEach循环，本次主要讲一下for循环和forEach循环。

for循环

break、continue都可以跳出多层嵌套循环

1. break是跳出此层循环，继续进行下一层循环；

for (int i = 0; i < 3; i++) {
            for (int j = 0; j < 3; j++) {
                if (j == 1) {
                    break;
                }
                System.out.println("i = " + i + ", j = " + j);

            }
        }

输出结果：
i = 0, j = 0
i = 1, j = 0
i = 2, j = 0

2. continue是跳出本次循环，继续进行下一次循环；

for (int i = 0; i < 3; i++) {
            for (int j = 0; j < 3; j++) {
                if (j == 1) {
                    continue;
                }
                System.out.println("i = " + i + ", j = " + j);

            }
        }

输出结果：
i = 0, j = 0
i = 0, j = 2
i = 1, j = 0
i = 1, j = 2
i = 2, j = 0
i = 2, j = 2

3. 外层循环条件表达式的结果可以受到里层循环体代码的控制，从而跳出指定层数；

ok:
        for (int i = 0; i < 10; i++) {
            for (int j = 0; j < 10; j++) {
                if (j == 5) {
                    break ok;
                }
                System.out.println("i = " + i + ", j = " + j);
            }
        }

输出结果：
i = 0, j = 0
i = 0, j = 1
i = 0, j = 2
i = 0, j = 3
i = 0, j = 4

4. 外层循环条件表达式的结果可以受到里层循环体代码的控制，使用正则表达式判断。这种方式在实际开发中比较常见，一定要掌握；
   continue；

int arr[][] = {{1,2,3,4},{5,6,7,8,9},{10,11}};
        boolean found = false;
        for (int i = 0; i < arr.length; i++) {
            for (int j = 0; j < arr[i].length; j++) {
                if (arr[i][j] == 5) {
                    found = true;
                    continue;
                }
                System.out.println("i = " + i + ", j = " + j);
            }
        }

输出结果：
i = 0, j = 0
i = 0, j = 1
i = 0, j = 2
i = 0, j = 3
i = 1, j = 1
i = 1, j = 2
i = 1, j = 3
i = 1, j = 4
i = 2, j = 0
i = 2, j = 1

break;

int arr[][] = {{1,2,3,4},{5,6,7,8,9},{10,11}};
        boolean found = false;
        for (int i = 0; i < arr.length; i++) {
            for (int j = 0; j < arr[i].length; j++) {
                if (arr[i][j] == 5) {
                    found = true;
                    break;
                }
                System.out.println("i = " + i + ", j = " + j);
            }
        }

输出结果：
i = 0, j = 0
i = 0, j = 1
i = 0, j = 2
i = 0, j = 3
i = 2, j = 0
i = 2, j = 1

5. 使用抛异常的方式，强制结束循环，我建议不要使用这种方法。这种虽然也可以结束循环，但是抛个异常，感觉有点耍流氓，实际开发没有用到过；

for (int i = 0; i < 10; i++) {
            for (int j = 0; j < 10; j++) {
                System.out.println("i = " + i + ", j = " + j);
                if (j == 5) {
                    throw new Exception("跳出多层循环");
                }
            }
        }

输出结果：
i = 0, j = 0
i = 0, j = 1
i = 0, j = 2
i = 0, j = 3
i = 0, j = 4
i = 0, j = 5
Exception in thread "main" java.lang.Exception: 跳出多层循环
	at com.java.basic.HelloWord.main(HelloWord.java:55)

forEach循环

1. 普通的froEach循环和上面的是一样的，这次只做break演示；

int arr[] = {1,2,3,4,5,6,7,8};
        for (int a:arr) {
            System.out.println("a = " + a);
            if (a == 5) {
                break;
            }
        }

输出结果：
a = 1
a = 2
a = 3
a = 4
a = 5

1. Java8中的特殊写法lambda表达式中，不能使用break和continue，会提示错误，Java8中使用return，会跳出当前循环，继续下一次循环，作用类似continue；
   
   

 //java8，forEach循环
        List<Student> list = new ArrayList<>();

        Student jack = new Student();
        jack.setName("jack");
        jack.setAge(18);
        jack.setGender("男");
        list.add(jack);

        Student jane = new Student();
        jane.setName("Jane");
        jane.setGender("女");
        jane.setAge(19);
        list.add(jane);

        Student lihua = new Student();
        lihua.setName("LiHua");
        lihua.setGender("男");
        lihua.setAge(20);
        list.add(lihua);

        list.forEach(student -> {
            if ("女".equals(student.getGender())) {
                return;
            }
            System.out.println("姓名：" + student.getName() + ", 性别：" + student.getGender() + ", 年龄：" + student.getAge());

        });

输出结果：
姓名：jack, 性别：男, 年龄：18
姓名：LiHua, 性别：男, 年龄：20

关于面试：这一部分属于基础知识部分，一定要特别熟练，面试官可能不经常问，感觉默认面试者是全部熟练掌握了，如果不熟练，一定要多练习，多看看！！！