Demonstrating Visibility

PackagePrivate.java

package org.codefx.lab.visibility;

class PackagePrivate {

	public String publicToUpper(String s) {
		return s.toUpperCase();
	}

	String packageToUpper(String s) {
		return s.toUpperCase();
	}

}

Public.java

package org.codefx.lab.visibility;

public class Public extends PackagePrivate { }

VisibilityTest.java

package org.codefx.lab.visibility.not;

import org.codefx.lab.visibility.Public;
import org.junit.Test;

import java.util.stream.Stream;

public class VisibilityTest {

	@Test
	public void toUpper() throws Exception {
		Public p = new Public();
		Stream.of("a", "b", "c")
				.map(p::publicToUpper)
				// next line is a compile error:
				// 		"The type org.codefx.lab.visibility.Public does not define packageToUpper(java.lang.String)
				// 		that is applicable here"
				// commenting it out makes the code compile and run
				.map(p::packageToUpper)
				.forEach(System.out::println);
	}

}

This reproduces the error:

public class VisibilityTest {

    @Test
    public void toUpper() throws Exception {
        final BiFunction<Public, String, String> publicStringStringBiFunction = Public::publicToUpper;

        // java.lang.IllegalAccessError: tried to access class org.codefx.lab.visibilityPackagePrivate from class org.codefx.lab.visibility.not.VisibilityTest
        publicStringStringBiFunction.apply(new Public(), "a");
    }

}