Java for循环之前声明for循环变量的写法及示例代码

1､将for语句的第一部分留空

int v = 0;
for (; v < 2; v++) {
    System.out.println(v);
Thread.sleep(1000); 
}

2､while (true)循环相同的写法

int v=1;
for (;;) {
System.out.println(v);
Thread.sleep(1000); 
}

3､多个变量的写法

int j = 0;
for (int k = 0; k < 10; k++, j++) {
}

或者

int j = 0;
for (int k = 0; k < 10 || j < 10; k++, j++) {
}

或者

for (int k = 0, j = 0; k < 10 || j < 10; k++, j++) {
}

4､简洁的写法

public class Main {
    public static void main(String[] args) {
        int[] integers = { 10, 20, 30 };
        for (int x : integers) {
            System.out.println(x);
        }
    }
}

5､for语句的一般形式

官方文档：https://docs.oracle.com/javase/tutorial/java/nutsandbolts/for.html

for (initialization; termination; increment) {
    statement(s)
}