Package access and protection

Java provides four access levels. Package‑private (default, no modifier) is the level when no explicit modifier is used. It allows access within the same package only.

Modifier	Class	Package	Subclass (different package)	World
private	✅	❌	❌	❌
(default)	✅	✅	❌	❌
protected	✅	✅	✅	❌
public	✅	✅	✅	✅

Package‑private example:

// File: com/example/util/Helper.java
package com.example.util;
class Helper {    // no modifier = package‑private
    void assist() { }
}

// File: com/example/main/Main.java
package com.example.main;
import com.example.util.Helper; // error: Helper not accessible (different package)

Same package access:

// Both in com.example.util
class Helper { void assist() { } }
class User {
    void use() {
        Helper h = new Helper(); // OK
        h.assist();              // OK
    }
}

Protected vs default: protected allows access in subclasses even in different packages.

Purpose: Package‑private is ideal for implementation details that should be visible within a package but not outside.

Module system (Java 9+) adds another layer: By default, types are not exported unless explicitly exported in module-info.java.