Java Package Visibility

JavaPackageVisibilityTest.java

package com.sivalabs.component_a;

//This is package-private, can't be accessed from outside of "com.sivalabs.component_a" package
class Mapper {
    public String toUpper(String input) {
        return input.toUpperCase();
    }
}

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package com.sivalabs.component_a;

import java.util.List;
import java.util.stream.Stream;

//This is a public package, can be accessed from anywhere.
public class ServiceA {
    private final Mapper mapper;

    public ServiceA(Mapper mapper) { //Intellij IDE also shows warninng "Class 'Mapper' is exposed outside its defined visibility scope "
        this.mapper = mapper;
    }

    public List<String> findAll() {
        return Stream.of("a", "b", "c")
            .map(mapper::toUpper).toList();
    }
}
-----------------------------------------
  
package com.sivalabs.component_b;

import com.sivalabs.component_a.ServiceA;

public class ServiceB {
    private final ServiceA serviceA;

    public ServiceB(ServiceA serviceA) {
        this.serviceA = serviceA;
    }

    public void printAll() {
        serviceA.findAll().forEach(System.out::println);
    }
}
-------------------------------------------
package com.sivalabs.component_b;


import com.sivalabs.component_a.Mapper;
import com.sivalabs.component_a.RepoA;
import com.sivalabs.component_a.ServiceA;
import org.junit.jupiter.api.Test;

class ServiceBTest {

    @Test
    void testPrintAll() {
        Mapper mapper = new Mapper(); //Can't access Mapper from component_b package
        ServiceA serviceA = new ServiceA(mapper);
        ServiceB serviceB = new ServiceB(serviceA);
        serviceB.printAll();
    }
}

Related Twitter Discussion: https://twitter.com/sivalabs/status/1764897093540618326