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Java 2 Platform SE v1.3.1: Class Method - JDK 5 Documentation v1.3.1, Java 2 SDK 英文文档

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JavaTM 2 Platform
Std. Ed. v1.3.1
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java.lang.reflect
Class Method

java.lang.Object
  |
  +--java.lang.reflect.AccessibleObject
        |
        +--java.lang.reflect.Method
All Implemented Interfaces:
Member
public final class Method
extends AccessibleObject
implements Member

A Method provides information about, and access to, a single method on a class or interface. The reflected method may be a class method or an instance method (including an abstract method).

A Method permits widening conversions to occur when matching the actual parameters to invokewith the underlying method's formal parameters, but it throws an IllegalArgumentException if a narrowing conversion would occur.

See Also:
Member, Class, Class.getMethods(), Class.getMethod(String, Class[]), Class.getDeclaredMethods(), Class.getDeclaredMethod(String, Class[])

Fields inherited from interface java.lang.reflect.Member
DECLARED, PUBLIC
 
Method Summary
 boolean equals(Object obj)
          Compares this Method against the specified object.
 Class getDeclaringClass()
          Returns the Class object representing the class or interface that declares the method represented by this Method object.
 Class[] getExceptionTypes()
          Returns an array of Class objects that represent the types of the exceptions declared to be thrown by the underlying method represented by this Method object.
 int getModifiers()
          Returns the Java language modifiers for the method represented by this Method object, as an integer.
 String getName()
          Returns the name of the method represented by this Method object, as a String.
 Class[] getParameterTypes()
          Returns an array of Class objects that represent the formal parameter types, in declaration order, of the method represented by this Method object.
 Class getReturnType()
          Returns a Class object that represents the formal return type of the method represented by this Method object.
 int hashCode()
          Returns a hashcode for this Method.
 Object invoke(Object obj, Object[] args)
          Invokes the underlying method represented by this Method object, on the specified object with the specified parameters.
 String toString()
          Returns a string describing this Method.
 
Methods inherited from class java.lang.reflect.AccessibleObject
isAccessible, setAccessible, setAccessible
 
Methods inherited from class java.lang.Object
clone, finalize, getClass, notify, notifyAll, wait, wait, wait
 

Method Detail

getDeclaringClass

public Class getDeclaringClass()
Returns the Class object representing the class or interface that declares the method represented by this Method object.
Specified by:
getDeclaringClass in interface Member

getName

public String getName()
Returns the name of the method represented by this Method object, as a String.
Specified by:
getName in interface Member

getModifiers

public int getModifiers()
Returns the Java language modifiers for the method represented by this Method object, as an integer. The Modifier class should be used to decode the modifiers.
Specified by:
getModifiers in interface Member
See Also:
Modifier

getReturnType

public Class getReturnType()
Returns a Class object that represents the formal return type of the method represented by this Method object.

getParameterTypes

public Class[] getParameterTypes()
Returns an array of Class objects that represent the formal parameter types, in declaration order, of the method represented by this Method object. Returns an array of length 0 if the underlying method takes no parameters.

getExceptionTypes

public Class[] getExceptionTypes()
Returns an array of Class objects that represent the types of the exceptions declared to be thrown by the underlying method represented by this Method object. Returns an array of length 0 if the method declares no exceptions in its throws clause.

equals

public boolean equals(Object obj)
Compares this Method against the specified object. Returns true if the objects are the same. Two Methods are the same if they were declared by the same class and have the same name and formal parameter types and return type.
Overrides:
equals in class Object
Following copied from class: java.lang.Object
Parameters:
obj - the reference object with which to compare.
Returns:
true if this object is the same as the obj argument; false otherwise.
See Also:
Boolean.hashCode(), Hashtable

hashCode

public int hashCode()
Returns a hashcode for this Method. The hashcode is computed as the exclusive-or of the hashcodes for the underlying method's declaring class name and the method's name.
Overrides:
hashCode in class Object
Following copied from class: java.lang.Object
Returns:
a hash code value for this object.
See Also:
Object.equals(java.lang.Object), Hashtable

toString

public String toString()
Returns a string describing this Method. The string is formatted as the method access modifiers, if any, followed by the method return type, followed by a space, followed by the class declaring the method, followed by a period, followed by the method name, followed by a parenthesized, comma-separated list of the method's formal parameter types. If the method throws checked exceptions, the parameter list is followed by a space, followed by the word throws followed by a comma-separated list of the thrown exception types. For example: 
    public boolean java.lang.Object.equals(java.lang.Object)

The access modifiers are placed in canonical order as specified by "The Java Language Specification". This is public, protected or private first, and then other modifiers in the following order: abstract, static, final, synchronized native.

Overrides:
toString in class Object
Following copied from class: java.lang.Object
Returns:
a string representation of the object.

invoke

public Object invoke(Object obj,
                     Object[] args)
              throws IllegalAccessException,
                     IllegalArgumentException,
                     InvocationTargetException
Invokes the underlying method represented by this Method object, on the specified object with the specified parameters. Individual parameters are automatically unwrapped to match primitive formal parameters, and both primitive and reference parameters are subject to widening conversions as necessary. The value returned by the underlying method is automatically wrapped in an object if it has a primitive type.

Method invocation proceeds with the following steps, in order:

If the underlying method is static, then the specified obj argument is ignored. It may be null.

Otherwise, the method is an instance method. If the specified object argument is null, the invocation throws a NullPointerException. Otherwise, if the specified object argument is not an instance of the class or interface declaring the underlying method (or of a subclass or implementor thereof) the invocation throws an IllegalArgumentException.

If this Method object enforces Java language access control and the underlying method is inaccessible, the invocation throws an IllegalAccessException.

If the number of actual parameters supplied via args is different from the number of formal parameters required by the underlying method, the invocation throws an IllegalArgumentException.

For each actual parameter in the supplied args array:

If the corresponding formal parameter has a primitive type, an unwrapping conversion is attempted to convert the object value to a value of a primitive type. If this attempt fails, the invocation throws an IllegalArgumentException.

If, after possible unwrapping, the parameter value cannot be converted to the corresponding formal parameter type by a method invocation conversion, the invocation throws an IllegalArgumentException.

If the underlying method is an instance method, it is invoked using dynamic method lookup as documented in The Java Language Specification, section 15.11.4.4; in particular, overriding based on the runtime type of the target object will occur.

If the underlying method is static, the class that declared the method is initialized if it has not already been initialized. The underlying method is invoked directly.

Control transfers to the invoked method. If the method completes abruptly by throwing an exception, the exception is placed in an InvocationTargetException and thrown in turn to the caller of invoke.

If the method completes normally, the value it returns is returned to the caller of invoke; if the value has a primitive type, it is first appropriately wrapped in an object. If the underlying method return type is void, the invocation returns null.

Throws:
IllegalAccessException - if the underlying method is inaccessible.
IllegalArgumentException - if the number of actual and formal parameters differ, or if an unwrapping conversion fails.
InvocationTargetException - if the underlying method throws an exception.
NullPointerException - if the specified object is null and the method is an instance method.
ExceptionInInitializerError - if the initialization provoked by this method fails.
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JavaTM 2 Platform
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For further API reference and developer documentation, see Java 2 SDK SE Developer Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.

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