Get the field represented by the supplied java.lang.reflect.Field field object on the specified Object target object . - Android java.lang.reflect

Android examples for java.lang.reflect:Field

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Description

Get the field represented by the supplied java.lang.reflect.Field field object on the specified Object target object .

Demo Code

/*/*  ww w  . j  a  v a  2s.com*/
 * Copyright 2002-2009 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
//package com.java2s;

import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;

public class Main {
    /**
     * Get the field represented by the supplied {@link java.lang.reflect.Field field object} on the
     * specified {@link Object target object}. In accordance with {@link java.lang.reflect.Field#get(Object)}
     * semantics, the returned value is automatically wrapped if the underlying field
     * has a primitive type.
     * <p>Thrown exceptions are handled via a call to {@link #handleReflectionException(Exception)}.
     * @param field the field to get
     * @param target the target object from which to get the field
     * @return the field's current value
     */
    public static Object getField(Field field, Object target) {
        try {
            return field.get(target);
        } catch (IllegalAccessException ex) {
            handleReflectionException(ex);
            throw new IllegalStateException(
                    "Unexpected reflection exception - "
                            + ex.getClass().getName() + ": "
                            + ex.getMessage());
        }
    }

    /**
     * Handle the given reflection exception. Should only be called if no
     * checked exception is expected to be thrown by the target method.
     * <p>Throws the underlying RuntimeException or Error in case of an
     * InvocationTargetException with such a root cause. Throws an
     * IllegalStateException with an appropriate message else.
     * @param ex the reflection exception to handle
     */
    public static void handleReflectionException(Exception ex) {
        if (ex instanceof NoSuchMethodException) {
            throw new IllegalStateException("Method not found: "
                    + ex.getMessage());
        }
        if (ex instanceof IllegalAccessException) {
            throw new IllegalStateException("Could not access method: "
                    + ex.getMessage());
        }
        if (ex instanceof InvocationTargetException) {
            handleInvocationTargetException((InvocationTargetException) ex);
        }
        if (ex instanceof RuntimeException) {
            throw (RuntimeException) ex;
        }
        handleUnexpectedException(ex);
    }

    /**
     * Handle the given invocation target exception. Should only be called if no
     * checked exception is expected to be thrown by the target method.
     * <p>Throws the underlying RuntimeException or Error in case of such a root
     * cause. Throws an IllegalStateException else.
     * @param ex the invocation target exception to handle
     */
    public static void handleInvocationTargetException(
            InvocationTargetException ex) {
        rethrowRuntimeException(ex.getTargetException());
    }

    /**
     * Throws an IllegalStateException with the given exception as root cause.
     * @param ex the unexpected exception
     */
    private static void handleUnexpectedException(Throwable ex) {
        throw new IllegalStateException("Unexpected exception thrown", ex);
    }

    /**
     * Rethrow the given {@link Throwable exception}, which is presumably the
     * <em>target exception</em> of an {@link java.lang.reflect.InvocationTargetException}. Should
     * only be called if no checked exception is expected to be thrown by the
     * target method.
     * <p>Rethrows the underlying exception cast to an {@link RuntimeException} or
     * {@link Error} if appropriate; otherwise, throws an
     * {@link IllegalStateException}.
     * @param ex the exception to rethrow
     * @throws RuntimeException the rethrown exception
     */
    public static void rethrowRuntimeException(Throwable ex) {
        if (ex instanceof RuntimeException) {
            throw (RuntimeException) ex;
        }
        if (ex instanceof Error) {
            throw (Error) ex;
        }
        handleUnexpectedException(ex);
    }
}

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