Explain packages in Java discuss access protection and importing packages with example.

 Explain packages in Java discuss access protection and importing packages with example.


 Packages in Java – Extended Explanation


✅ What is a Package in Java?

A package in Java is a collection of related classes, interfaces, and sub-packages grouped together.

👉 Simple meaning:
Package = Folder
Classes = Files inside folder

It helps to:

organize code properly

avoid name conflicts

provide security (access control)

reuse code easily

---
🔹 Types of Packages

1. Built-in (Predefined) Packages

Already provided by Java.

Examples:

java.lang

java.util

java.io

java.sql


Example:

import java.util.Scanner;


---

2. User-Defined Packages

Created by programmer.

Example:

package mypack;


---

🔹 How to Create a Package?

Step 1: Write package statement

package mypack;

Step 2: Create class

package mypack;

public class Message {
    public void show() {
        System.out.println("Hello Nami!");
    }
}

Step 3: Compile

javac -d . Message.java

👉 -d . creates folder automatically


---

🔹 Advantages of Packages

✅ Code organization
✅ Avoid class name duplication
✅ Easy maintenance
✅ Security using access protection
✅ Reusability


---

🔹 Access Protection in Packages

Java provides 4 access modifiers to protect data.

Modifier Same Class Same Package Subclass Other Package

private ✅ ❌ ❌ ❌
default ✅ ✅ ❌ ❌
protected ✅ ✅ ✅ ❌*
public ✅ ✅ ✅ ✅



---

1️⃣ Private

Accessible only inside same class

class Test {
    private int x = 10;
}

👉 Cannot access outside class


---

2️⃣ Default (no modifier)

Accessible only inside same package

class Test {
    int x = 20;
}

👉 Works inside same package only


---

3️⃣ Protected

Accessible:

same package

subclass (even different package)


protected int x = 30;


---

4️⃣ Public

Accessible everywhere

public int x = 40;


---

🔹 Example for Access Protection

Package: mypack

package mypack;

public class AccessDemo {
    private int a = 10;
    int b = 20;
    protected int c = 30;
    public int d = 40;

    public void display() {
        System.out.println(a + " " + b + " " + c + " " + d);
    }
}


---

Another class in same package

package mypack;

class Test {
    public static void main(String[] args) {
        AccessDemo obj = new AccessDemo();

        // System.out.println(obj.a); ❌ private
        System.out.println(obj.b); // ✅
        System.out.println(obj.c); // ✅
        System.out.println(obj.d); // ✅
    }
}


---

🔹 Importing Packages

To use classes from another package, we use import keyword.


---

Types of Import

1️⃣ Import single class

import java.util.Scanner;


---

2️⃣ Import all classes

import java.util.*;


---

3️⃣ Fully qualified name (no import)

java.util.Scanner sc = new java.util.Scanner(System.in);


---

🔹 Example Program using Import

import java.util.Scanner;

public class InputDemo {
    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);

        System.out.println("Enter your name:");
        String name = sc.nextLine();

        System.out.println("Hello " + name);
    }
}


---

🔹 Complete Example with User Defined Package

Step 1: Create package class

File: mypack/Calculator.java

package mypack;

public class Calculator {

    public int add(int a, int b) {
        return a + b;
    }
}


---

Step 2: Use package in another class

File: Main.java

import mypack.Calculator;

class Main {
    public static void main(String[] args) {

        Calculator obj = new Calculator();

        int result = obj.add(5, 3);

        System.out.println("Sum = " + result);
    }
}


---

🔹 Compilation Steps

javac -d . Calculator.java
javac Main.java
java Main

Output:

Sum = 8

---

✅ Final Conclusion

Packages in Java help to:

group related classes
avoid naming conflicts
provide access protection
improve security
make large projects manageable

Access modifiers control visibility, and import allows using classes from other packages easily.


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