Modifiers Types in Java

Modifiers are keywords that you add to those definitions to change their meanings.
The Java language has a wide variety of modifiers, including the following:

1. Java Access Modifiers
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).

Default Access Modifier No keyword:
Default access modifier means we do not explicitly declare an access modifier for a class, field, method etc.
A variable or method declared without any access control modifier is available to any other class in the same package. The default modifier cannot be used for methods, fields in an interface.
Example:
String version = "1.5.1";
boolean processOrder() {
return true;
}

Private Access Modifier Private:
Methods, Variables and Constructors that are declared private can only be accessed within the declared lass itself.
Private access modifier is the most restrictive access level. Class and interfaces cannot be private.
Variables that are declared private can be accessed outside the class if public getter methods are present in the class.

Example:
public class Logger {
private String format;
public String getFormat() {
return this.format;
}
public void setFormat(String format) {
this.format = format;
}
}

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 need to be imported.

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

Protected Access Modifier Protected:
Variables, methods and constructors which are declared protected in a super class can be accessed only by the subclasses in other package or any class within the package of the protected members' class.
The protected access modifier cannot be applied to class and interfaces. Methods, fields can be declared protected, however methods and fields in a interface cannot be declared protected.

Example:
class AudioPlayer {
protected boolean openSpeaker(Speaker sp) {
}
}
class StreamingAudioPlayer {
boolean openSpeaker(Speaker sp) {
}
}

Access Control and Inheritance:
The following rules for inherited methods are enforced:

• Methods declared public in a super class also must be public in all subclasses.
• Methods declared protected in a super class must either be protected or public in subclasses; they cannot be private.
• Methods declared without access control (no modifier was used) can be declared more private in subclasses.
• Methods declared private are not inherited at all, so there is no rule for them.

2. Non Access Modifiers
To use a modifier, you include its keyword in the definition of a class, method, or variable. The modifier precedes the rest of the statement, as in the following examples (Italic ones):
public class className {
// ...
}
private boolean myFlag;
static final double weeks = 9.5;
protected static final int BOXWIDTH = 42;
public static void main(String[] arguments) {
// body of method
}

Access Control Modifiers:
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).

Non Access Modifiers:
Java provides a number of non-access modifiers to achieve many other functionality.

• The static modifier for creating class methods and variables.
• The final modifier for finalizing the implementations of classes, methods, and variables.
• The abstract modifier for creating abstract classes and methods.
• The synchronized and volatile modifiers, which are used for threads.