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A Java class can be declared with an access modifier to specify how it will be accessed by the other classes in Java, and this access modifier is known as class access modifier. Let us see different kinds of class access modifiers.

• Public Access Modifier


When a class is declared with the public keyword, it means that this class is accessible and visible to all the classes in all the packages in Java. Out of all the access modifiers, public access modifier gives a class, the maximum visibility. Let's see an example-

A.java

public class A
{
}

B.java

class B
{
public static void main(String... ar)
{
A ob= new A();
}
}

• In this code, we have created two classes, A(in A.java)and B(in B.java)
• Class A is declared public and that's why it is visible and accessible to the class B. Hence, there is no compile error when B.java is compiled, even though it is accessing class A and creating its object.







Note :


To use a public class declared in a different package, you will still have to import it.






There can be only public class defined in one .java file


There can only be one public class defined in a .java file, and the name of this class should match with the name of .java file in which it is defined and saved, otherwise Java Compiler will throw a compiler error.

A1.java

public class A
{
public static void main(String...ar)
{
System.out.println("Hello");
}
}



On compiling this class, we have received a compile error :

D:\Java>javac A1.java
A1.java:1: error: class A is public, should be declared in a file named A.java
public class A
       ^
1 error






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• Default Access Modifier


When you declare a class with no access modifier, it is automatically given a default access modifier or default visibility, which means that this class is accessible and visible only to the classes in the same package. That's why it is also referred to as a - package level access. Let's understand this by an example -






When two default classes exist in the same package


A.java

package pack1;

class A 
{
}

B.java

package pack1;

class B
{
public static void main(String... ar)
{
A ob = new A();
}
}

Class A and class B exist in the package, pack1. Hence, when class A was accessed in the code of B class, we have received no compile error in the compilation of B.java.






When two default classes exist in the different package


If you try to access a default class from a class that belongs to a different package, it would lead to a compile error. Let's understand this by an example -

A.java

package pack1;

class A 
{
}

B.java

package pack2;

class B
{
public static void main(String... ar)
{
A ob = new A();
}
}

After compiling :

B.java:7: error: cannot find symbol
A ob = new A();
^
  symbol:   class A
  location: class B
B.java:7: error: cannot find symbol
A ob = new A();
           ^
  symbol:   class A
  location: class B
2 errors
}

Class A exists in the package, pack1, while Class B exists in the package, pack2. Hence, we have received compile errors on the compilation of B.java, clearly stating that the compiler couldn't find class A when accessed in the code of B.java





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