Prompt Title: Java Private Classes.

Sure, let's consider a scenario where we have two packages - com.packagea and com.packageb. We also have three classes - Class1, Class2, and Class3. Here's an example code that illustrates the different visibility scenarios:

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// File: Class1.java
package com.packagea;

public class Class1 {
    // Public method
    public void method1() {
        System.out.println("Method1 in Class1");
    }
}

// File: Class2.java
package com.packagea;

class Class2 {
    // Default method
    void method2() {
        System.out.println("Method2 in Class2");
    }
}

// File: Class3.java
package com.packageb;

public class Class3 {
    // Public method
    public void method3() {
        System.out.println("Method3 in Class3");
    }
}

In this example, Class1 is declared as public, so it is visible to both com.packagea and com.packageb. Class2 is declared with default visibility, so it is only visible to other classes in the same package (com.packagea). Class3 is declared as public, but it is in a different package than Class1 and Class2, so it is only visible to com.packageb.

Now, let's create a test class in each package to demonstrate the visibility:

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// File: TestClass1.java
package com.packagea;

import com.packageb.Class3;

public class TestClass1 {
    public static void main(String[] args) {
        // Create instances of all three classes
        Class1 class1 = new Class1();
        Class2 class2 = new Class2();
        Class3 class3 = new Class3();

        // Call methods on Class1 and Class2
        class1.method1();
        class2.method2();

        // Try to call method on Class3 - this will result in a compile-time error
        //class3.method3(); // This line will not compile
    }
}

// File: TestClass2.java
package com.packageb;

import com.packagea.Class1;
import com.packagea.Class2;

public class TestClass2 {
    public static void main(String[] args) {
        // Create instances of all three classes
        Class1 class1 = new Class1();
        Class2 class2 = new Class2();
        Class3 class3 = new Class3();

        // Call method on Class3
        class3.method3();

        // Try to call methods on Class1 and Class2 - these will result in compile-time errors
        //class1.method1(); // This line will not compile
        //class2.method2(); // This line will not compile
    }
}

In TestClass1, we can create instances of all three classes and call methods on Class1 and Class2 because they are visible in the same package as TestClass1. However, we cannot call the method on Class3 because it is in a different package and not visible to TestClass1.

In TestClass2, we can create instances of all three classes and call the method on Class3 because it is visible to the same package as TestClass2. However, we cannot call methods on Class1 and Class2 because they are in a different package and not visible to TestClass2.