Java - public keyword

Java provides a number of access modifiers to set access levels for classes, variables, methods, and constructors. The four access levels are −

• Visible to the package, the default. No modifiers are needed.

• Visible to the class only (private).

• Visible to the world (public).

• Visible to the package and all subclasses (protected).

Access Control and Inheritance

The following rules for inherited methods are enforced −

• Methods declared public in a superclass also must be public in all subclasses.

• Methods declared protected in a superclass must either be protected or public in subclasses; they cannot be private.

• Methods declared private are not inherited at all, so there is no rule for them.

Public Access Modifier - Public

A class, method, constructor, interface, etc. declared public can be accessed from any other class. Therefore, fields, methods, blocks declared inside a public class can be accessed from any class belonging to the Java Universe.

However, if the public class we are trying to access is in a different package, then the public class still needs to be imported. Because of class inheritance, all public methods and variables of a class are inherited by its subclasses.

Example

The following function uses public access control −

 public static void main(String[] arguments) { // ... } 

The main() method of an application has to be public. Otherwise, it could not be called by a Java interpreter (such as java) to run the class.

Example

The following class uses public access control. We've used a public field as shown below −

 package com.tutorialspoint; public class JavaTester { public String format; public String getFormat() { return this.format; } public void setFormat(String format) { this.format = format; } public void print() { System.out.println(this.format); } public static void main(String args[]) { JavaTester tester = new JavaTester(); tester.format = "XML"; } } 

Output

 XML 

Here, the format variable of the Logger class is public, so this variable can be accessed directly using just a reference of the class Logger.

But as a best practice, to make this variable available to the outside world, we defined two public methods: getFormat(), which returns the value of format, and setFormat(String), which sets its value.

Following is another example of public access identifier. We've defined a public field in super class. If a field/method is public then it can be inherited by subclass.

Example

 package com.tutorialspoint; class Logger { public String format; public void print() { System.out.println(this.format); } } public class JavaTester extends Logger { public static void main(String args[]) { JavaTester tester = new JavaTester(); tester.format = "XML"; tester.print(); } } 

Output

 XML