java.lang.reflect.Field Maven / Gradle / Ivy

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This work corresponds to the API signatures of JSR 219: Foundation Profile 1.1. In the event of a discrepency between this work and the JSR 219 specification, which is available at http://www.jcp.org/en/jsr/detail?id=219, the latter takes precedence. */ package java.lang.reflect; /** * A Field provides information about, and dynamic access to, a * single field of a class or an interface. The reflected field may * be a class (static) field or an instance field. * *

A Field permits widening conversions to occur during a get or * set access operation, but throws an IllegalArgumentException if a * narrowing conversion would occur. * * @see Member * @see java.lang.Class * @see java.lang.Class#getFields() * @see java.lang.Class#getField(String) * @see java.lang.Class#getDeclaredFields() * @see java.lang.Class#getDeclaredField(String) * * @author Nakul Saraiya */ public final class Field extends AccessibleObject implements Member { /* * This hidden constructor does not necessarily correspond to * a constructor in the original source file -- it keeps javadoc * from generating an inappropriate default constructor. */ private Field() { } /** * Returns the Class object representing the class or interface * that declares the field represented by this Field object. */ public Class getDeclaringClass() { return null; } /** * Returns the name of the field represented by this Field object. */ public String getName() { return null; } /** * Returns the Java language modifiers for the field represented * by this Field object, as an integer. The Modifier class should * be used to decode the modifiers. * * @see Modifier */ public int getModifiers() { return 0; } /** * Returns a Class object that identifies the * declared type for the field represented by this * Field object. * * @return a Class object identifying the declared * type of the field represented by this object */ public Class getType() { return null; } /** * Compares this Field against the specified object. Returns * true if the objects are the same. Two Field objects are the same if * they were declared by the same class and have the same name * and type. */ public boolean equals(Object obj) { return false; } /** * Returns a hashcode for this Field. This is computed as the * exclusive-or of the hashcodes for the underlying field's * declaring class name and its name. */ public int hashCode() { return 0; } /** * Returns a string describing this Field. The format is * the access modifiers for the field, if any, followed * by the field type, followed by a space, followed by * the fully-qualified name of the class declaring the field, * followed by a period, followed by the name of the field. * For example: *

     *    public static final int java.lang.Thread.MIN_PRIORITY
     *    private int java.io.FileDescriptor.fd
     * 

The 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: static, final, * transient, volatile. */ public String toString() { return null; } /** * Returns the value of the field represented by this Field, on * the specified object. The value is automatically wrapped in an * object if it has a primitive type. * *

The underlying field's value is obtained as follows: * *

If the underlying field is a static field, the obj argument * is ignored; it may be null. * *

Otherwise, the underlying field is an instance field. If the * specified obj argument is null, the method throws a * NullPointerException. If the specified object is not an * instance of the class or interface declaring the underlying * field, the method throws an IllegalArgumentException. * *

If this Field object enforces Java language access control, and * the underlying field is inaccessible, the method throws an * IllegalAccessException. * If the underlying field is static, the class that declared the * field is initialized if it has not already been initialized. * *

Otherwise, the value is retrieved from the underlying instance * or static field. If the field has a primitive type, the value * is wrapped in an object before being returned, otherwise it is * returned as is. * *

If the field is hidden in the type of obj, * the field's value is obtained according to the preceding rules. * * @param obj object from which the represented field's value is * to be extracted * @return the value of the represented field in object * obj; primitive values are wrapped in an appropriate * object before being returned * * @exception IllegalAccessException if the underlying field * is inaccessible. * @exception IllegalArgumentException if the specified object is not an * instance of the class or interface declaring the underlying * field (or a subclass or implementor thereof). * @exception NullPointerException if the specified object is null * and the field is an instance field. * @exception ExceptionInInitializerError if the initialization provoked * by this method fails. */ public Object get(Object obj) throws IllegalArgumentException, IllegalAccessException { return null; } /** * Gets the value of a static or instance boolean field. * * @param obj the object to extract the boolean value * from * @return the value of the boolean field * * @exception IllegalAccessException if the underlying field * is inaccessible. * @exception IllegalArgumentException if the specified object is not * an instance of the class or interface declaring the * underlying field (or a subclass or implementor * thereof), or if the field value cannot be * converted to the type boolean by a * widening conversion. * @exception NullPointerException if the specified object is null * and the field is an instance field. * @exception ExceptionInInitializerError if the initialization provoked * by this method fails. * @see Field#get */ public boolean getBoolean(Object obj) throws IllegalArgumentException, IllegalAccessException { return false; } /** * Gets the value of a static or instance byte field. * * @param obj the object to extract the byte value * from * @return the value of the byte field * * @exception IllegalAccessException if the underlying field * is inaccessible. * @exception IllegalArgumentException if the specified object is not * an instance of the class or interface declaring the * underlying field (or a subclass or implementor * thereof), or if the field value cannot be * converted to the type byte by a * widening conversion. * @exception NullPointerException if the specified object is null * and the field is an instance field. * @exception ExceptionInInitializerError if the initialization provoked * by this method fails. * @see Field#get */ public byte getByte(Object obj) throws IllegalArgumentException, IllegalAccessException { return ' '; } /** * Gets the value of a static or instance field of type * char or of another primitive type convertible to * type char via a widening conversion. * * @param obj the object to extract the char value * from * @return the value of the field converted to type char * * @exception IllegalAccessException if the underlying field * is inaccessible. * @exception IllegalArgumentException if the specified object is not * an instance of the class or interface declaring the * underlying field (or a subclass or implementor * thereof), or if the field value cannot be * converted to the type char by a * widening conversion. * @exception NullPointerException if the specified object is null * and the field is an instance field. * @exception ExceptionInInitializerError if the initialization provoked * by this method fails. * @see Field#get */ public char getChar(Object obj) throws IllegalArgumentException, IllegalAccessException { return ' '; } /** * Gets the value of a static or instance field of type * short or of another primitive type convertible to * type short via a widening conversion. * * @param obj the object to extract the short value * from * @return the value of the field converted to type short * * @exception IllegalAccessException if the underlying field * is inaccessible. * @exception IllegalArgumentException if the specified object is not * an instance of the class or interface declaring the * underlying field (or a subclass or implementor * thereof), or if the field value cannot be * converted to the type short by a * widening conversion. * @exception NullPointerException if the specified object is null * and the field is an instance field. * @exception ExceptionInInitializerError if the initialization provoked * by this method fails. * @see Field#get */ public short getShort(Object obj) throws IllegalArgumentException, IllegalAccessException { return -1; } /** * Gets the value of a static or instance field of type * int or of another primitive type convertible to * type int via a widening conversion. * * @param obj the object to extract the int value * from * @return the value of the field converted to type int * * @exception IllegalAccessException if the underlying field * is inaccessible. * @exception IllegalArgumentException if the specified object is not * an instance of the class or interface declaring the * underlying field (or a subclass or implementor * thereof), or if the field value cannot be * converted to the type int by a * widening conversion. * @exception NullPointerException if the specified object is null * and the field is an instance field. * @exception ExceptionInInitializerError if the initialization provoked * by this method fails. * @see Field#get */ public int getInt(Object obj) throws IllegalArgumentException, IllegalAccessException { return 0; } /** * Gets the value of a static or instance field of type * long or of another primitive type convertible to * type long via a widening conversion. * * @param obj the object to extract the long value * from * @return the value of the field converted to type long * * @exception IllegalAccessException if the underlying field * is inaccessible. * @exception IllegalArgumentException if the specified object is not * an instance of the class or interface declaring the * underlying field (or a subclass or implementor * thereof), or if the field value cannot be * converted to the type long by a * widening conversion. * @exception NullPointerException if the specified object is null * and the field is an instance field. * @exception ExceptionInInitializerError if the initialization provoked * by this method fails. * @see Field#get */ public long getLong(Object obj) throws IllegalArgumentException, IllegalAccessException { return -1; } /** * Gets the value of a static or instance field of type * float or of another primitive type convertible to * type float via a widening conversion. * * @param obj the object to extract the float value * from * @return the value of the field converted to type float * * @exception IllegalAccessException if the underlying field * is inaccessible. * @exception IllegalArgumentException if the specified object is not * an instance of the class or interface declaring the * underlying field (or a subclass or implementor * thereof), or if the field value cannot be * converted to the type float by a * widening conversion. * @exception NullPointerException if the specified object is null * and the field is an instance field. * @exception ExceptionInInitializerError if the initialization provoked * by this method fails. * @see Field#get */ public float getFloat(Object obj) throws IllegalArgumentException, IllegalAccessException { return 0.0f; } /** * Gets the value of a static or instance field of type * double or of another primitive type convertible to * type double via a widening conversion. * * @param obj the object to extract the double value * from * @return the value of the field converted to type double * * @exception IllegalAccessException if the underlying field * is inaccessible. * @exception IllegalArgumentException if the specified object is not * an instance of the class or interface declaring the * underlying field (or a subclass or implementor * thereof), or if the field value cannot be * converted to the type double by a * widening conversion. * @exception NullPointerException if the specified object is null * and the field is an instance field. * @exception ExceptionInInitializerError if the initialization provoked * by this method fails. * @see Field#get */ public double getDouble(Object obj) throws IllegalArgumentException, IllegalAccessException { return 0.0d; } /** * Sets the field represented by this Field object on the * specified object argument to the specified new value. The new * value is automatically unwrapped if the underlying field has a * primitive type. * *

The operation proceeds as follows: * *

If the underlying field is static, the obj argument is * ignored; it may be null. * *

Otherwise the underlying field is an instance field. If the * specified object argument is null, the method throws a * NullPointerException. If the specified object argument is not * an instance of the class or interface declaring the underlying * field, the method throws an IllegalArgumentException. * *

If this Field object enforces Java language access control, and * the underlying field is inaccessible, the method throws an * IllegalAccessException. * *

If the underlying field is final, the method throws an * IllegalAccessException. * *

If the underlying field is of a primitive type, an unwrapping * conversion is attempted to convert the new value to a value of * a primitive type. If this attempt fails, the method throws an * IllegalArgumentException. * *

If, after possible unwrapping, the new value cannot be * converted to the type of the underlying field by an identity or * widening conversion, the method throws an * IllegalArgumentException. * *

If the underlying field is static, the class that declared the * field is initialized if it has not already been initialized. * *

The field is set to the possibly unwrapped and widened new value. * *