get and set methods in java

• Static variables information need to access with static get() methods.
• Non static variables information need to access with non static get() methods.

class Test
{
	private int a ;
	public int getA()
	{
		return this.a ;
	}
}
public class Access
{
	public static void main(String args[ ])
	{
		Test obj = new Test();
		// System.out.println("a value : " + obj.a);  -> Error : private access
		System.out.println("a value : " + obj.getA());
	}
}

Following diagram explains where to access private modifier in Java:

private class Program
{
	/* logic */
}
Compiler throws error when we compile above code

Why a class cannot be private?

• A class represents object.
• Private members can be accessed with in the class (by same object itself).
• If class is private, the entire object is not visible to outside world for communication. Hence it is useless of defining a class using private modifier.

Private constructor: If constructor is private, we cannot instantiate the class from other classes.

class First
{
	First()
	{
		System.out.println("First class object created");

	}
}
class Second
{
	public static void main(String args[ ])
	{
		new First();
	}
}

Trying to create object with private constructor:

class First
{
	private First()
	{
		System.out.println("First class object created");

	}
}
class Second
{
	public static void main(String args[ ])
	{
		new First(); //Error : Cannot create object.
	}
}

• We cannot instantiate a class in java without constructor call. In the definition of Singleton and Factory class design patterns we use private constructor.
• We request the object using static method.
• Once we get the object, we access the non static functionality using that object.

class First
{
	private First()
	{
		System.out.println("First class object created");
	}
	void fun()
	{
		System.out.println("First class functionality");
	}
	static First getObject()
	{
		return new First();
	}
}
class Second
{
	public static void main(String args[ ])
	{
		First obj = First.getObject(); // request for object
		obj.fun(); // access the functionality
	}
}

Sample code:

class Sample
{
	static void m1(){
		System.out.println("Sample class static method");
	}
	void m2(){
		System.out.println("Sample calss non static method");
	}
	private Sample(){
		System.out.println("Sample object created...");
	}
	static Sample getObject(){
		Sample obj = new Sample();
		return obj;
	}
}
public class Test 
{
	public static void main(String args[ ])
	{
		Sample.m1();
		// Sample addr = new Sample(); // Error : cannot create object directly.
		Sample addr = Sample.getObject();  // collect object address on request
		addr.m2();
	}
}