Java – why is string:: isempty valid when a static context cannot reference a non static method?

I understand the error message I know I cannot access non - static methods in a static context But why can I do the following:

Predicate<String> t = String::isEmpty; // this works

When isempty() is a non static method of string class? View the following sample classes I understand the logic that testlamba:: isemptytest is not allowed; But I don't understand why string: isempty can break this rule:

import java.util.function.Predicate;

public class TestLamba {

    public static void main(String... args) {

        Predicate<String> t = String::isEmpty; // this works
        Predicate<String> t2 = TestLamba::isEmptyTest; // this doesn't
    }

    public boolean isEmptytest() {
        return true;
    }

}

This is string Isempty source code This is a very common method. You can see that it is not static:

public boolean isEmpty() {
    return this.value.length == 0;
}

Solution

Isempty is a function of string class and isemptytest is a function of testlamba class

import java.util.function.Predicate;

public class TestLamba {

    public static void main(String... args) {

        Predicate<String> t = String::isEmpty; // this works
        Predicate<TestLamba > t2 = TestLamba::isEmptyTest; // this Now will work
    }

    public boolean isEmptytest() {
        return true;
    }

}