Java Control Statements

Java Control Statements

Java For Loop

public class ForExample1 {
    public static void main(String[] args) {
        // Java for loop
        for (int i = 1; i <= 10; i++) {
            System.out.println(i);
        }
    }
}

运行结果

```
1
2
3
4
5
6
7
8
9
10
```

public class ForExample2 {
    public static void main(String[] args) {
        // 无限 for 循环
        for (; ; ) {
            System.out.println("infinitive loop");
        }
    }
}

运行结果

```
死循环...
```

public class ForEachExample1 {
    public static void main(String[] args) {
        int arr[] = {12, 23, 44, 56, 78};
        // for-each loop
        for (int i : arr) {
            System.out.println(i);
        }
    }
}

运行结果

```
12
23
44
56
78
```

import java.util.Arrays;
import java.util.List;

public class ForEachExample2 {
    public static void main(String[] args) {
        List<Integer> list = Arrays.asList(12, 23, 44, 56, 78);
        list.stream().forEach((i) -> System.out.println(i));
    }
}

运行结果

```
12
23
44
56
78
```

public class LabeledForExample1 {
    public static void main(String[] args) {
        aa:
        for (int i = 1; i <= 3; i++) {
            bb:
            for (int j = 1; j <= 3; j++) {
                if (i == 2 && j == 2) {
                    break aa;
                    // break bb;
                }
                System.out.println(i + " " + j);
            }
        }
    }
}

运行结果

```
1 1
1 2
1 3
2 1
```

public class LabeledForExample2 {
    public static void main(String[] args) {
        aa:
        for (int i = 1; i <= 3; i++) {
            bb:
            for (int j = 1; j <= 3; j++) {
                if (i == 2 && j == 2) {
                    // break aa;
                    break bb;
                }
                System.out.println(i + " " + j);
            }
        }
    }
}

运行结果

```
1 1
1 2
1 3
2 1
3 1
3 2
3 3
```

Java While Loop

public class WhileExample1 {
    public static void main(String[] args) {
        int i = 1;
        while (i <= 10) {
            System.out.println(i);
            i++;
        }
    }
}

运行结果

```
1
2
3
4
5
6
7
8
9
10
```

public class WhileExample2 {
    public static void main(String[] args) {
        while (true) {
            System.out.println("infinitive while loop");
        }
    }
}

运行结果

```
死循环...
```

Java Do While Loop

public class DoWhileExample1 {
    public static void main(String[] args) {
        int i = 1;
        do {
            System.out.println(i);
            i++;
        } while (i <= 10);
    }
}

运行结果

```
1
2
3
4
5
6
7
8
9
10
```

public class DoWhileExample2 {
    public static void main(String[] args) {
        do {
            System.out.println("infinitive do while loop");
        } while (true);
    }
}

运行结果

```
死循环...
```

Java Break

public class BreakExample1 {
    public static void main(String[] args) {
        for (int i = 1; i <= 10; i++) {
            if (i == 5) {
                break;
            }
            System.out.println(i);
        }
    }
}

运行结果

```
1
2
3
4
```

public class BreakExample2 {
    public static void main(String[] args) {
        // outer loop
        for (int i = 1; i <= 3; i++) {
            // inner loop
            for (int j = 1; j <= 3; j++) {
                if (i == 2 && j == 2) {
                    // using break statement inside the inner loop
                    break;
                }
                System.out.println(i + " " + j);
            }
        }
    }
}

运行结果

```
1 1
1 2
1 3
2 1
3 1
3 2
3 3
```

public class BreakExample3 {
    public static void main(String[] args) {
        aa:
        for (int i = 1; i <= 3; i++) {
            bb:
            for (int j = 1; j <= 3; j++) {
                if (i == 2 && j == 2) {
                    break aa;
                }
                System.out.println(i + " " + j);
            }
        }
    }
}

运行结果

```
1 1
1 2
1 3
2 1
```

public class BreakWhileExample {
    public static void main(String[] args) {
        int i = 1;
        while (i <= 10) {
            if (i == 5) {
                i++;
                break;
            }
            System.out.println(i);
            i++;
        }
    }
}

运行结果

```
1
2
3
4
```

public class BreakDoWhileExample {
    public static void main(String[] args) {
        int i = 1;
        do {
            if (i == 5) {
                i++;
                break;
            }
            System.out.println(i);
            i++;
        } while (i <= 10);
    }
}

运行结果

```
1
2
3
4
```

Java Continue

public class ContinueExample1 {
    public static void main(String[] args) {
        for (int i = 1; i <= 10; i++) {
            if (i == 5) {
                continue;
            }
            System.out.println(i);
        }
    }
}

运行结果

```
1
2
3
4
6
7
8
9
10
```

public class ContinueExample2 {
    public static void main(String[] args) {
        for (int i = 1; i <= 3; i++) {
            for (int j = 1; j <= 3; j++) {
                if (i == 2 && j == 2) {
                    continue;
                }
                System.out.println(i + " " + j);
            }
        }
    }
}

运行结果

```
1 1
1 2
1 3
2 1
2 3
3 1
3 2
3 3
```

public class ContinueExample3 {
    public static void main(String[] args) {
        aa:
        for (int i = 1; i <= 3; i++) {
            bb:
            for (int j = 1; j <= 3; j++) {
                if (i == 2 && j == 2) {
                    continue aa;
                }
                System.out.println(i + " " + j);
            }
        }
    }
}

运行结果

```
1 1
1 2
1 3
2 1
3 1
3 2
3 3
```

public class ContinueWhileExample {
    public static void main(String[] args) {
        int i = 1;
        while (i <= 10) {
            if (i == 5) {
                i++;
                continue;
            }
            System.out.println(i);
            i++;
        }
    }
}

运行结果

```
1
2
3
4
6
7
8
9
10
```

public class ContinueDoWhileExample {
    public static void main(String[] args) {
        int i = 1;
        do {
            if (i == 5) {
                i++;
                continue;
            }
            System.out.println(i);
            i++;
        } while (i <= 10);
    }
}

运行结果

```
1
2
3
4
6
7
8
9
10
```

break 和 continue 的作用

• 1、当循环执行到 break 语句时，就退出整个循环，然后执行循环外的语句。
• 2、当循环语句执行到 continue 时，当次循环结束，重新开始下一轮循环。如果已经是最后一轮循环了，那么这是的 continue 就与 break 效果一样了。

参考资料

• https://docs.oracle.com/javase/tutorial/java/nutsandbolts/branch.html
• https://www.javatpoint.com/java-tutorial