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Java Fundamental Classes Reference

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13. The java.lang.reflect Package

The package java.lang.reflect is new as of Java 1.1. It contains classes and interfaces that support the Reflection API. Reflection refers to the ability of a class to reflect upon itself, or look inside of itself, to see what it can do. The Reflection API makes it possible to:

  • Discover the variables, methods, and constructors of any class.

  • Create an instance of any class using any available constructor of that class, even if the class initiating the creation was not compiled with any information about the class to be instantiated.

  • Access the variables of any object, even if the accessing class was not compiled with any information about the class to be accessed.

  • Call the methods of any object, even if the calling class was not compiled with any information about the class that contains the methods.

  • Create an array of objects that are instances of any class, even if the creating class was not compiled with any information about the class.

These capabilities are implemented by the java.lang.Class class and the classes in the java.lang.reflect package. Figure 13.1 shows the class hierarchy for the java.lang.reflect package.

Java 1.1 currently uses the Reflection API for two purposes:

  • The JavaBeans API supports a mechanism for customizing objects that is based on being able to discover their public variables, methods, and constructors. See the forthcoming Developing Java Beans from O'Reilly & Associates for more information about the JavaBeans API.

  • The object serialization functionality in java.io is built on top of the Reflection API. Object serialization allows arbitrary objects to be written to a stream of bytes and then read back later as objects.

Array

Name

Array

Synopsis

Class Name:

java.lang.reflect.Array

Superclass:

java.lang.Object

Immediate Subclasses:

None

Interfaces Implemented:

java.lang.Cloneable, java.io.Serializable

Availability:

New as of JDK 1.1

Description

The Array class provides static methods to manipulate arbitrary arrays in Java. There are methods to set and retrieve elements in an array, determine the size of an array, and create a new instance of an array.

The Array class is used to create array objects and manipulate their elements. The Array class is not used to represent array types. Because arrays in Java are objects, array types are represented by Class objects.

Class Summary

public final class java.lang.reflect.Array extends java.lang.Object {
  // Class Methods
  public static native Object get(Object array, int index);
  public static native boolean getBoolean(Object array, int index);
  public static native byte getByte(Object array, int index);
  public static native char getChar(Object array, int index);
  public static native double getDouble(Object array, int index);
  public static native float getFloat(Object array, int index);
  public static native int getInt(Object array, int index);
  public static native int getLength(Object array);
  public static native long getLong(Object array, int index);
  public static native short getShort(Object array, int index);
  public static Object newInstance(Class componentType, int length);
  public static Object newInstance(Class componentType, int[] dimensions);
  public static native void set(Object array, int index, Object value);
  public static native void setBoolean(Object array, int index, boolean z);
  public static native void setByte(Object array, int index, byte b);
  public static native void setChar(Object array, int index, char c);
  public static native void setDouble(Object array, int index, double d);
  public static native void setFloat(Object array, int index, float f);
  public static native void setInt(Object array, int index, int i);
  public static native void setLong(Object array, int index, long l);
  public static native void setShort(Object array, int index, short s);
}

Class Methods

get

 public static native Object get(Object array, int index) throws IllegalArgumentException, ArrayIndexOutOfBoundsException 

Parameters

array

An array object.

index

An index into the array.

Returns

The object at the given index in the specified array.

Throws

IllegalArgumentException

If the given object is not an array.

ArrayIndexOutOfBoundsException

If the given index is invalid.

NullPointerException

If array is null.

Description

This method returns the object at the given index in the array. If the array contains values of a primitive type, the value at the given index is wrapped in an appropriate object, and the object is returned.

getBoolean

 public static native boolean getBoolean(Object array, int index) throws IllegalArgumentException, ArrayIndexOutOfBoundsException 

Parameters

array

An array object.

index

An index into the array.

Returns

The boolean value at the given index in the specified array.

Throws

IllegalArgumentException

If the given object is not an array, or the object at the given index cannot be converted to a boolean.

ArrayIndexOutOfBoundsException

If the given index is invalid.

NullPointerException

If array is null.

Description

This method returns the object at the given index in the array as a boolean value.

getByte

 public static native byte getByte(Object array, int index) throws IllegalArgumentException, ArrayIndexOutOfBoundsException 

Parameters

array

An array object.

index

An index into the array.

Returns

The byte value at the given index in the specified array.

Throws

IllegalArgumentException

If the given object is not an array, or the object at the given index cannot be converted to a byte.

ArrayIndexOutOfBoundsException

If the given index is invalid.

NullPointerException

If array is null.

Description

This method returns the object at the given index in the array as a byte value.

getChar

 public static native char getChar(Object array, int index) throws IllegalArgumentException, ArrayIndexOutOfBoundsException 

Parameters

array

An array object.

index

An index into the array.

Returns

The char value at the given index in the specified array.

Throws

IllegalArgumentException

If the given object is not an array, or the object at the given index cannot be converted to a char.

ArrayIndexOutOfBoundsException

If the given index is invalid.

NullPointerException

If array is null.

Description

This method returns the object at the given index in the array as a char value.

getDouble

 public static native double getDouble(Object array, int index) throws IllegalArgumentException, ArrayIndexOutOfBoundsException 

Parameters

array

An array object.

index

An index into the array.

Returns

The double value at the given index in the specified array.

Throws

IllegalArgumentException

If the given object is not an array, or the object at the given index cannot be converted to a double.

ArrayIndexOutOfBoundsException

If the given index is invalid.

NullPointerException

If array is null.

Description

This method returns the object at the given index in the array as a double value.

getFloat

 public static native float getFloat(Object array, int index) throws IllegalArgumentException, ArrayIndexOutOfBoundsException 

Parameters

array

An array object.

index

An index into the array.

Returns

The float value at the given index in the specified array.

Throws

IllegalArgumentException

If the given object is not an array, or the object at the given index cannot be converted to a float.

ArrayIndexOutOfBoundsException

If the given index is invalid.

NullPointerException

If array is null.

Description

This method returns the object at the given index in the array as a float value.

getInt

 public static native int getInt(Object array, int index) throws IllegalArgumentException, ArrayIndexOutOfBoundsException 

Parameters

array

An array object.

index

An index into the array.

Returns

The int value at the given index in the specified array.

Throws

IllegalArgumentException

If the given object is not an array, or the object at the given index cannot be converted to a int.

ArrayIndexOutOfBoundsException

If the given index is invalid.

NullPointerException

If array is null.

Description

This method returns the object at the given index in the array as a int value.

getLength

 public static native int getLength(Object array) throws IllegalArgumentException 

Parameters

array

An array object.

Returns

The length of the specified array.

Throws

IllegalArgumentException

If the given object is not an array.

Description

This method returns the length of the array.

getLong

 public static native long getLong(Object array, long index) throws IllegalArgumentException, ArrayIndexOutOfBoundsException 

Parameters

array

An array object.

index

An index into the array.

Returns

The long value at the given index in the specified array.

Throws

IllegalArgumentException

If the given object is not an array, or the object at the given index cannot be converted to a long.

ArrayIndexOutOfBoundsException

If the given index is invalid.

NullPointerException

If array is null.

Description

This method returns the object at the given index in the array as a long value.

getShort

 public static native short getShort(Object array, short index) throws IllegalArgumentException, ArrayIndexOutOfBoundsException 

Parameters

array

An array object.

index

An index into the array.

Returns

The short value at the given index in the specified array.

Throws

IllegalArgumentException

If the given object is not an array, or the object at the given index cannot be converted to a short.

ArrayIndexOutOfBoundsException

If the given index is invalid.

NullPointerException

If array is null.

Description

This method returns the object at the given index in the array as a short value.

newInstance

 public static Object newInstance(Class componentType, int length) throws NegativeArraySizeException 

Parameters

componentType

The type of each element in the array.

length

The length of the array.

Returns

An array object that contains elements of the given component type and has the specified length.

Throws

NegativeArraySizeException

If length is negative.

NullPointerException

If componentType is null.

Description

This method creates a single-dimension array with the given length and component type.

 public static Object newInstance(Class componentType, int[] dimensions) throws IllegalArgumentException, NegativeArraySizeException 

Parameters

componentType

The type of each element in the array.

dimensions

An array that specifies the dimensions of the array to be created.

Returns

An array object that contains elements of the given component type and has the specified number of dimensions.

Throws

IllegalArgumentException

If dimensions has zero dimensions itself, or if it has too many dimensions (typically 255 array dimensions are supported).

NegativeArraySizeException

If length is negative.

NullPointerException

If componentType is null.

Description

This method creates a multidimensional array with the given dimensions and component type.

set

 public static native void set(Object array, int index, Object value) throws IllegalArgumentException, ArrayIndexOutOfBoundsException 

Parameters

array

An array object.

index

An index into the array.

value

The new value.

Throws

IllegalArgumentException

If the given object is not an array, or if it represents an array of primitive values, and the given value cannot be unwrapped and converted to that primitive type.

ArrayIndexOutOfBoundsException

If the given index is invalid.

NullPointerException

If array is null.

Description

This method sets the object at the given index in the array to the specified value. If the array contains values of a primitive type, the given value is automatically unwrapped before it is put in the array.

setBoolean

 public static native void setBoolean(Object array, int index, boolean z) throws IllegalArgumentException, ArrayIndexOutOfBoundsException 

Parameters

array

An array object.

index

An index into the array.

z

The new value.

Throws

IllegalArgumentException

If the given object is not an array, or if the given value cannot be converted to the component type of the array.

ArrayIndexOutOfBoundsException

If the given index is invalid.

NullPointerException

If array is null.

Description

This method sets the element at the given index in the array to the given boolean value.

setByte

 public static native void setByte(Object array, int index, byte b) throws IllegalArgumentException, ArrayIndexOutOfBoundsException 

Parameters

array

An array object.

index

An index into the array.

b

The new value.

Throws

IllegalArgumentException

If the given object is not an array, or if the given value cannot be converted to the component type of the array.

ArrayIndexOutOfBoundsException

If the given index is invalid.

NullPointerException

If array is null.

Description

This method sets the element at the given index in the array to the given byte value.

setChar

 public static native void setChar(Object array, int index, char c) throws IllegalArgumentException, ArrayIndexOutOfBoundsException 

Parameters

array

An array object.

index

An index into the array.

c

The new value.

Throws

IllegalArgumentException

If the given object is not an array, or if the given value cannot be converted to the component type of the array.

ArrayIndexOutOfBoundsException

If the given index is invalid.

NullPointerException

If array is null.

Description

This method sets the element at the given index in the array to the given char value.

setDouble

 public static native void setDouble(Object array, int index, double d) throws IllegalArgumentException, ArrayIndexOutOfBoundsException 

Parameters

array

An array object.

index

An index into the array.

d

The new value.

Throws

IllegalArgumentException

If the given object is not an array, or if the given value cannot be converted to the component type of the array.

ArrayIndexOutOfBoundsException

If the given index is invalid.

NullPointerException

If array is null.

Description

This method sets the element at the given index in the array to the given double value.

setFloat

 public static native void setFloat(Object array, int index, float f) throws IllegalArgumentException, ArrayIndexOutOfBoundsException 

Parameters

array

An array object.

index

An index into the array.

f

The new value.

Throws

IllegalArgumentException

If the given object is not an array, or if the given value cannot be converted to the component type of the array.

ArrayIndexOutOfBoundsException

If the given index is invalid.

NullPointerException

If array is null.

Description

This method sets the element at the given index in the array to the given float value.

setInt

 public static native void setInt(Object array, int index, int i) throws IllegalArgumentException, ArrayIndexOutOfBoundsException 

Parameters

array

An array object.

index

An index into the array.

i

The new value.

Throws

IllegalArgumentException

If the given object is not an array, or if the given value cannot be converted to the component type of the array.

ArrayIndexOutOfBoundsException

If the given index is invalid.

NullPointerException

If array is null.

Description

This method sets the element at the given index in the array to the given int value.

setLong

 public static native void setLong(Object array, int index, long l) throws IllegalArgumentException, ArrayIndexOutOfBoundsException 

Parameters

array

An array object.

index

An index into the array.

l

The new value.

Throws

IllegalArgumentException

If the given object is not an array, or if the given value cannot be converted to the component type of the array.

ArrayIndexOutOfBoundsException

If the given index is invalid.

NullPointerException

If array is null.

Description

This method sets the element at the given index in the array to the given long value.

setShort

 public static native void setShort(Object array, int index, short s) throws IllegalArgumentException, ArrayIndexOutOfBoundsException 

Parameters

array

An array object.

index

An index into the array.

s

The new value.

Throws

IllegalArgumentException

If the given object is not an array, or if the given value cannot be converted to the component type of the array.

ArrayIndexOutOfBoundsException

If the given index is invalid.

NullPointerException

If array is null.

Description

This method sets the element at the given index in the array to the given short value.

Inherited Methods

Method

Inherited From

Method

Inherited From

clone()

Object

equals(Object)

Object

finalize()

Object

getClass()

Object

hashCode()

Object

notify()

Object

notifyAll()

Object

toString()

Object

wait()

Object

wait(long)

Object

wait(long, int)

Object

   

See Also

ArrayIndexOutOfBoundsException, Class, IllegalArgumentException, NegativeArraySizeException, NullPointerException, Object


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