Java Class New Instance newInstance(Class theClass, Class expected)

Description

Create an object for the given class and initialize it from conf

License

Apache License

Parameter

Parameter	Description
theClass	class of which an object is created
expected	the expected parent class or interface

Return

a new object

Declaration

public static <T> T newInstance(Class<?> theClass, Class<T> expected) 

Method Source Code

//package com.java2s;
/*/*from ww w. j a  v  a 2  s .c o  m*/
 * Copyright 2012, Facebook, Inc.
 *
 * 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.
 */

import java.lang.reflect.Constructor;

public class Main {
    private static final Class<?>[] EMPTY_ARRAY = new Class[] {};

    /** Create an object for the given class and initialize it from conf
     *
     * @param theClass class of which an object is created
     * @param expected the expected parent class or interface
     * @return a new object
     */
    public static <T> T newInstance(Class<?> theClass, Class<T> expected) {
        T result;
        try {
            if (!expected.isAssignableFrom(theClass)) {
                throw new Exception("Specified class " + theClass.getName() + "" + "does not extend/implement "
                        + expected.getName());
            }
            Class<? extends T> clazz = (Class<? extends T>) theClass;
            Constructor<? extends T> meth = clazz.getDeclaredConstructor(EMPTY_ARRAY);
            meth.setAccessible(true);
            result = meth.newInstance();
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
        return result;
    }

    public static <T> T newInstance(String className, Class<T> expected) throws ClassNotFoundException {
        return newInstance(getClassByName(className), expected);
    }

    /**
     * Load a class by name.
     * @param name the class name.
     * @return the class object.
     * @throws ClassNotFoundException if the class is not found.
     */
    public static Class<?> getClassByName(String name) throws ClassNotFoundException {
        ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
        return Class.forName(name, true, classLoader);
    }
}

Related

1. newInstance(Class cls)
2. newInstance(Class cls)
3. newInstance(Class cls, Map, Constructor> cache)
4. newInstance(Class componentType, int... dimensions)
5. newInstance(Class entity)
6. newInstance(Class interfaceDefinition, String className, ClassLoader classLoader)
7. newInstance(Class aClass, Object... args)
8. newInstance(Class arrayComponentClass, T value)
9. newInstance(Class beanClass)