The Java Tutorials have been written for JDK 8. Examples and practices described in this page don't take advantage of improvements introduced in later releases and might use technology no longer available.
See Java Language Changes for a summary of updated language features in Java SE 9 and subsequent releases.
See JDK Release Notes for information about new features, enhancements, and removed or deprecated options for all JDK releases.
There a several modifiers that may be part of a method declaration:
public
, protected
, and private
static
final
abstract
synchronized
native
strictfp
The
example lists the modifiers of a method with a given name. It also displays whether the method is synthetic (compiler-generated), of variable arity, or a bridge method (compiler-generated to support generic interfaces).MethodModifierSpy
import java.lang.reflect.Method; import java.lang.reflect.Modifier; import static java.lang.System.out; public class MethodModifierSpy { private static int count; private static synchronized void inc() { count++; } private static synchronized int cnt() { return count; } public static void main(String... args) { try { Class<?> c = Class.forName(args[0]); Method[] allMethods = c.getDeclaredMethods(); for (Method m : allMethods) { if (!m.getName().equals(args[1])) { continue; } out.format("%s%n", m.toGenericString()); out.format(" Modifiers: %s%n", Modifier.toString(m.getModifiers())); out.format(" [ synthetic=%-5b var_args=%-5b bridge=%-5b ]%n", m.isSynthetic(), m.isVarArgs(), m.isBridge()); inc(); } out.format("%d matching overload%s found%n", cnt(), (cnt() == 1 ? "" : "s")); // production code should handle this exception more gracefully } catch (ClassNotFoundException x) { x.printStackTrace(); } } }
A few examples of the output
produces follow.MethodModifierSpy
$ java MethodModifierSpy java.lang.Object wait public final void java.lang.Object.wait() throws java.lang.InterruptedException Modifiers: public final [ synthetic=false var_args=false bridge=false ] public final void java.lang.Object.wait(long,int) throws java.lang.InterruptedException Modifiers: public final [ synthetic=false var_args=false bridge=false ] public final native void java.lang.Object.wait(long) throws java.lang.InterruptedException Modifiers: public final native [ synthetic=false var_args=false bridge=false ] 3 matching overloads found
$ java MethodModifierSpy java.lang.StrictMath toRadians public static double java.lang.StrictMath.toRadians(double) Modifiers: public static strictfp [ synthetic=false var_args=false bridge=false ] 1 matching overload found
$ java MethodModifierSpy MethodModifierSpy inc private synchronized void MethodModifierSpy.inc() Modifiers: private synchronized [ synthetic=false var_args=false bridge=false ] 1 matching overload found
$ java MethodModifierSpy java.lang.Class getConstructor public java.lang.reflect.Constructor<T> java.lang.Class.getConstructor (java.lang.Class<T>[]) throws java.lang.NoSuchMethodException, java.lang.SecurityException Modifiers: public transient [ synthetic=false var_args=true bridge=false ] 1 matching overload found
$ java MethodModifierSpy java.lang.String compareTo public int java.lang.String.compareTo(java.lang.String) Modifiers: public [ synthetic=false var_args=false bridge=false ] public int java.lang.String.compareTo(java.lang.Object) Modifiers: public volatile [ synthetic=true var_args=false bridge=true ] 2 matching overloads found
Note that
Method.isVarArgs()
returns true
for
Class.getConstructor()
. This indicates that the method declaration looks like this:
public Constructor<T> getConstructor(Class<?>... parameterTypes)
not like this:
public Constructor<T> getConstructor(Class<?> [] parameterTypes)
Notice that the output for
String.compareTo()
contains two methods. The method declared in String.java
:
public int compareTo(String anotherString);
and a second synthetic or compiler-generated bridge method. This occurs because
String
implements the parameterized interface
Comparable
. During type erasure, the argument type of the inherited method
Comparable.compareTo()
is changed from java.lang.Object
to java.lang.String
. Since the parameter types for the compareTo
methods in Comparable
and String
no longer match after erasure, overriding can not occur. In all other circumstances, this would produce a compile-time error because the interface is not implemented. The addition of the bridge method avoids this problem.
Method
implements
java.lang.reflect.AnnotatedElement
. Thus any runtime annotations with
java.lang.annotation.RetentionPolicy.RUNTIME
may be retrieved. For an example of obtaining annotations see the section Examining Class Modifiers and Types.