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Java Fundamental Classes Reference

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The java.lang.reflect Package
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Field

Name

Field

Synopsis

Class Name:

java.lang.reflect.Field

Superclass:

java.lang.Object

Immediate Subclasses:

None

Interfaces Implemented:

java.lang.reflect.Member

Availability:

New as of JDK 1.1

Description

The Field class represents a variable or constant in a class. A Field object can be obtained by calling the getField() method of a Class object. Field includes methods for getting the name, modifiers, type, and declaring class of a field. The class also provides methods that can set and retrieve the value of a field for a particular object.

Class Summary

public final class java.lang.reflect.Field extends java.lang.Object
                   implements java.lang.reflect.Member {
  // Instance Methods
  public boolean equals(Object obj); 
  public native Object get(Object obj);
  public native boolean getBoolean(Object obj);
  public native byte getByte(Object obj);
  public native char getChar(Object obj);
  public Class getDeclaringClass();
  public native double getDouble(Object obj);
  public native float getFloat(Object obj);
  public native int getInt(Object obj);
  public native long getLong(Object obj);
  public native int getModifiers();
  public String getName();
  public native short getShort(Object obj);
  public Class getType();
  public int hashCode();
  public native void set(Object obj, Object value);
  public native void setBoolean(Object obj, boolean z);
  public native void setByte(Object obj, byte b);
  public native void setChar(Object obj, char c);
  public native void setDouble(Object obj, double d);
  public native void setFloat(Object obj, float f);
  public native void setInt(Object obj, int i);
  public native void setLong(Object obj, long l);
  public native void setShort(Object obj, short s);
  public String toString();
}

Instance Methods

equals

public boolean equals(Object obj)

Parameters

obj

The object to be compared with this object.

Returns

true if the objects are equal; false if they are not.

Overrides

Object.equals()

Description

This method returns true if obj is an instance of Field, and it is equivalent to this Field.

get

 public native Object get(Object obj) throws IllegalArgumentException, IllegalAccessException 

Parameters

obj

The instance whose field value is to be retrieved.

Returns

The value of this field in the given object.

Throws

IllegalArgumentException

If obj is not the correct type.

IllegalAccessException

If the field is not accessible.

NullPointerException

If obj is null.

Description

This method returns the value of this field in the given object. If the field is declared static, the obj parameter is ignored. Otherwise, the object supplied must be an instance of the class that declares this field. If the field contains a value of a primitive type, the value is wrapped in an appropriate object, and the object is returned.

getBoolean

 public native boolean getBoolean(Object obj) throws IllegalArgumentException, IllegalAccessException 

Parameters

obj

The instance whose field value is to be retrieved.

Returns

The boolean value of this field in the given object.

Throws

IllegalArgumentException

If obj is not the correct type, or the field cannot be converted to a boolean.

IllegalAccessException

If the field is not accessible.

NullPointerException

If obj is null.

Description

This method returns the value of this field in the given object as a boolean. If the field is declared static, the obj parameter is ignored. Otherwise, the object supplied must be an instance of the class that declares this field.

getByte

 public native byte getByte(Object obj) throws IllegalArgumentException, IllegalAccessException 

Parameters

obj

The instance whose field value is to be retrieved.

Returns

The byte value of this field in the given object.

Throws

IllegalArgumentException

If obj is not the correct type, or the field cannot be converted to a byte.

IllegalAccessException

If the field is not accessible.

NullPointerException

If obj is null.

Description

This method returns the value of this field in the given object as a byte. If the field is declared static, the obj parameter is ignored. Otherwise, the object supplied must be an instance of the class that declares this field.

getChar

 public native char getChar(Object obj) throws IllegalArgumentException, IllegalAccessException 

Parameters

obj

The instance whose field value is to be retrieved.

Returns

The char value of this field in the given object.

Throws

IllegalArgumentException

If obj is not the correct type, or the field cannot be converted to a char.

IllegalAccessException

If the field is not accessible.

NullPointerException

If obj is null.

Description

This method returns the value of this field in the given object as a char. If the field is declared static, the obj parameter is ignored. Otherwise, the object supplied must be an instance of the class that declares this field.

getDeclaringClass

public Class getDeclaringClass()

Returns

The Class object that represents the class that declared this field.

Implements

Member.getDeclaringClass()

Description

This method returns the Class object for the class in which this field is declared.

getDouble

 public native double getDouble(Object obj) throws IllegalArgumentException, IllegalAccessException 

Parameters

obj

The instance whose field value is to be retrieved.

Returns

The double value of this field in the given object.

Throws

IllegalArgumentException

If obj is not the correct type, or the field cannot be converted to a double.

IllegalAccessException

If the field is not accessible.

NullPointerException

If obj is null.

Description

This method returns the value of this field in the given object as a double. If the field is declared static, the obj parameter is ignored. Otherwise, the object supplied must be an instance of the class that declares this field.

getFloat

 public native float getFloat(Object obj) throws IllegalArgumentException, IllegalAccessException 

Parameters

obj

The instance whose field value is to be retrieved.

Returns

The float value of this field in the given object.

Throws

IllegalArgumentException

If obj is not the correct type, or the field cannot be converted to a float.

IllegalAccessException

If the field is not accessible.

NullPointerException

If obj is null.

Description

This method returns the value of this field in the given object as a float. If the field is declared static, the obj parameter is ignored. Otherwise, the object supplied must be an instance of the class that declares this field.

getInt

 public native int getInt(Object obj) throws IllegalArgumentException, IllegalAccessException 

Parameters

obj

The instance whose field value is to be retrieved.

Returns

The int value of this field in the given object.

Throws

IllegalArgumentException

If obj is not the correct type, or the field cannot be converted to a int.

IllegalAccessException

If the field is not accessible.

NullPointerException

If obj is null.

Description

This method returns the value of this field in the given object as an int. If the field is declared static, the obj parameter is ignored. Otherwise, the object supplied must be an instance of the class that declares this field.

getLong

 public native long getLong(Object obj) throws IllegalArgumentException, IllegalAccessException 

Parameters

obj

The instance whose field value is to be retrieved.

Returns

The long value of this field in the given object.

Throws

IllegalArgumentException

If obj is not the correct type, or the field cannot be converted to a long.

IllegalAccessException

If the field is not accessible.

NullPointerException

If obj is null.

Description

This method returns the value of this field in the given object as a long. If the field is declared static, the obj parameter is ignored. Otherwise, the object supplied must be an instance of the class that declares this field.

getModifiers

public native int getModifiers()

Returns

An integer that represents the modifier keywords used to declare this field.

Implements

Member.getModifiers()

Description

This method returns an integer value that represents the modifiers of this field. The Modifier class should decode the returned value.

getName

public String getName()

Returns

The name of this field as a String.

Implements

Member.getName()

Description

This method returns the name of this field.

getShort

 public native short getShort(Object obj) throws IllegalArgumentException, IllegalAccessException 

Parameters

obj

The instance whose field value is to be retrieved.

Returns

The short value of this field in the given object.

Throws

IllegalArgumentException

If obj is not the correct type, or the field cannot be converted to a short.

IllegalAccessException

If the field is not accessible.

NullPointerException

If obj is null.

Description

This method returns the value of this field in the given object as a short. If the field is declared static, the obj parameter is ignored. Otherwise, the object supplied must be an instance of the class that declares this field.

getType

public Class getType()

Returns

The Class object that represents the type of this field.

Description

This method returns the Class object for the type of this field.

hashCode

public int hashCode()

Returns

A hashcode for this object.

Overrides

Object.hashCode()

Description

This method returns a hashcode for this Field.

set

 public native void set(Object obj, Object value) throws IllegalArgumentException, IllegalAccessException 

Parameters

obj

The instance whose field value is to be set.

value

The new value.

Throws

IllegalArgumentException

If obj is not an instance of the correct class, or value cannot be converted to the correct type.

IllegalAccessException

If the field is not accessible or declared final.

NullPointerException

If obj is null.

Description

This method sets the value of this field in the given object to the given value. If the field is declared static, the obj parameter is ignored. Otherwise, the object supplied must be an instance of the class that declares this field. If the field contains a value of a primitive type, the given value is automatically unwrapped before it is used to set the value of the field.

setBoolean

 public native void setBoolean(Object obj, boolean z) throws IllegalArgumentException, IllegalAccessException 

Parameters

obj

The instance whose field value is to be set.

z

The new value.

Throws

IllegalArgumentException

If obj is not an instance of the correct class, or z cannot be converted to the correct type.

IllegalAccessException

If the field is not accessible or declared final.

NullPointerException

If obj is null.

Description

This method sets the value of this field in the given object to the given boolean value. If the field is declared static, the obj parameter is ignored. Otherwise, the object supplied must be an instance of the class that declares this field.

setByte

 public native void setByte(Object obj, byte b) throws IllegalArgumentException, IllegalAccessException 

Parameters

obj

The instance whose field value is to be set.

b

The new value.

Throws

IllegalArgumentException

If obj is not an instance of the correct class, or b cannot be converted to the correct type.

IllegalAccessException

If the field is not accessible or declared final.

NullPointerException

If obj is null.

Description

This method sets the value of this field in the given object to the given byte value. If the field is declared static, the obj parameter is ignored. Otherwise, the object supplied must be an instance of the class that declares this field.

setChar

 public native void setChar(Object obj, char c) throws IllegalArgumentException, IllegalAccessException 

Parameters

obj

The instance whose field value is to be set.

c

The new value.

Throws

IllegalArgumentException

If obj is not an instance of the correct class, or c cannot be converted to the correct type.

IllegalAccessException

If the field is not accessible or declared final.

NullPointerException

If obj is null.

Description

This method sets the value of this field in the given object to the given char value. If the field is declared static, the obj parameter is ignored. Otherwise, the object supplied must be an instance of the class that declares this field.

setDouble

 public native void setDouble(Object obj, double d) throws IllegalArgumentException, IllegalAccessException 

Parameters

obj

The instance whose field value is to be set.

d

The new value.

Throws

IllegalArgumentException

If obj is not an instance of the correct class, or d cannot be converted to the correct type.

IllegalAccessException

If the field is not accessible or declared final.

NullPointerException

If obj is null.

Description

This method sets the value of this field in the given object to the given double value. If the field is declared static, the obj parameter is ignored. Otherwise, the object supplied must be an instance of the class that declares this field.

setFloat

 public native void setFloat(Object obj, float f) throws IllegalArgumentException, IllegalAccessException 

Parameters

obj

The instance whose field value is to be set.

f

The new value.

Throws

IllegalArgumentException

If obj is not an instance of the correct class, or f cannot be converted to the correct type.

IllegalAccessException

If the field is not accessible or declared final.

NullPointerException

If obj is null.

Description

This method sets the value of this field in the given object to the given float value. If the field is declared static, the obj parameter is ignored. Otherwise, the object supplied must be an instance of the class that declares this field.

setInt

 public native void setInt(Object obj, int i) throws IllegalArgumentException, IllegalAccessException 

Parameters

obj

The instance whose field value is to be set.

i

The new value.

Throws

IllegalArgumentException

If obj is not an instance of the correct class, or i cannot be converted to the correct type.

IllegalAccessException

If the field is not accessible or declared final.

NullPointerException

If obj is null.

Description

This method sets the value of this field in the given object to the given int value. If the field is declared static, the obj parameter is ignored. Otherwise, the object supplied must be an instance of the class that declares this field.

setLong

 public native void setLong(Object obj, long l) throws IllegalArgumentException, IllegalAccessException 

Parameters

obj

The instance whose field value is to be set.

l

The new value.

Throws

IllegalArgumentException

If obj is not an instance of the correct class, or l cannot be converted to the correct type.

IllegalAccessException

If the field is not accessible or declared final.

NullPointerException

If obj is null.

Description

This method sets the value of this field in the given object to the given long value. If the field is declared static, the obj parameter is ignored. Otherwise, the object supplied must be an instance of the class that declares this field.

setShort

 public native void setShort(Object obj, short s) throws IllegalArgumentException, IllegalAccessException 

Parameters

obj

The instance whose field value is to be set.

s

The new value.

Throws

IllegalArgumentException

If obj is not an instance of the correct class, or s cannot be converted to the correct type.

IllegalAccessException

If the field is not accessible or declared final.

NullPointerException

If obj is null.

Description

This method sets the value of this field in the given object to the given short value. If the field is declared static, the obj parameter is ignored. Otherwise, the object supplied must be an instance of the class that declares this field.

toString

public String toString()

Returns

A string representation of this object.

Overrides

Object.toString()

Description

This method returns a string representation of this Field. This string contains the access modifiers of the field, if any, followed by the type, the fully qualified name of the declaring class, a period, and the name of the field.

Inherited Methods

Method

Inherited From

Method

Inherited From

clone()

Object

finalize()

Object

getClass()

Object

notify()

Object

notifyAll()

Object

wait()

Object

wait(long)

Object

wait(long, int)

Object

See Also

Class, Constructor, IllegalAccessException, IllegalArgumentException, Member, Method, Modifier, NullPointerException, Object


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