Modifiers

Modifier Used on Meaning
abstract class The class contains unimplemented methods and cannot be instantiated.
interface All interfaces are abstract. The modifier is optional in interface declarations.
abstract method No body is provided for the method; it is provided by a subclass. The signature is followed by a semicolon. The enclosing class must also be abstract.
final class The class cannot be subclassed.
method The method cannot be overridden (and is not subject to dynamic method lookup).
field The field cannot have its value changed. static final fields are compile-time constants.
variable A local variable, method parameter, or exception parameter cannot have its value changed ( Java 1.1 and later). Useful with local classes.
native method The method is implemented in some platform-dependent way (often in C). No body is provided; the signature is followed by a semicolon.
none (package) class A non-public class is accessible only in its package.
interface A non-public interface is accessible only in its package.
member A member that is not private, protected, or public has package visibility and is accessible only within its package.
private member The member is accessible only within the class that defines it.
protected member The member is accessible only within the package in which it is defined and within subclasses.
public class The class is accessible anywhere its package is.
interface The interface is accessible anywhere its package is.
member The member is accessible anywhere its class is.
strictfp class All methods of the class are implicitly strictfp ( Java 1.2 and later).
strictfp method All floating-point computation done by the method must be performed in a way that strictly conforms to the IEEE 754 standard. In particular, all values, including intermediate results, must be expressed as IEEE float or double values and cannot take advantage of any extra precision or range offered by native platform floating-point formats or hardware ( Java 1.2 and later). This modifier is rarely used.
static class An inner class declared static is a top-level class, not associated with a member of the containing class (Java 1.1 and later).
method A static method is a class method. It is not passed an implicit this object reference. It can be invoked through the class name.
field A static field is a class field. There is only one instance of the field, regardless of the number of class instances created. It can be accessed through the class name.
initializer The initializer is run when the class is loaded, rather than when an instance is created.
synchronized method The method makes non-atomic modifications to the class or instance, so care must be taken to ensure that two threads cannot modify the class or instance at the same time. For a static method, a lock for the class is acquired before executing the method. For a non-static method, a lock for the specific object instance is acquired.
transient field The field is not part of the persistent state of the object and should not be serialized with the object. Used with object serialization; see java.io.ObjectOutputStream.
volatile field The field can be accessed by unsynchronized threads, so certain optimizations must not be performed on it. This modifier can sometimes be used as an alternative to synchronized. This modifier is very rarely used.

Rules

  • a method declaration can contain only one of the access modifiers publicprotected and private
  • classes cannot be declared abstract and final simultaneously
  • abstract methods cannot be declared privatestaticfinalnativestrictfp or synchronized
  • methods cannot be declared native and strictfp simultaneously
  • abstract and native methods have no body
    • abstract void method();
    • native void method();
  • a class that contains abstract method(s) must be declared abstract
  • final fields cannot be volatile