public class Test {
    static Runnable r;

    public static void main(String... args) {
        r = () -> r.run();
        r.run();
    }
}

Runnable在运行时从字段r获取对其自身的引用.

The Runnable obtains a reference to itself from the field r when it is run.

如果您不喜欢添加字段，也可以使用长度为1的数组来存储引用.

You could also use a length 1 array to store the reference if you don't like adding a field.