Java Class New Instance newInstance(Class clazz)

Description

new Instance

License

Apache License

Declaration

public static <T> T newInstance(Class<T> clazz) 

Method Source Code

//package com.java2s;
/*/*w w  w  . ja v  a  2 s.  c o  m*/
 * Copyright [2013-2015] PayPal Software Foundation
 *
 * 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;

import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

public class Main {
    /**
     * Only support constructors with no parameters.
     */
    public static final Class<?>[] EMPTY_CLASS_ARRAY = new Class[] {};
    /**
     * This map is used for cache <class, constructor> pairs
     */
    private static final Map<Class<?>, Constructor<?>> CONSTRUCTOR_CACHE = new ConcurrentHashMap<Class<?>, Constructor<?>>();

    public static <T> T newInstance(Class<T> clazz) {
        T result;
        try {
            @SuppressWarnings("unchecked")
            Constructor<T> meth = (Constructor<T>) CONSTRUCTOR_CACHE.get(clazz);
            if (meth == null) {
                meth = clazz.getDeclaredConstructor(EMPTY_CLASS_ARRAY);
                meth.setAccessible(true);
                CONSTRUCTOR_CACHE.put(clazz, meth);
            }
            result = meth.newInstance();
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
        return result;
    }

    public static <T> T newInstance(Class<T> clazz, Class<?>[] parameterClasses, Object[] parameters) {
        T result;
        try {
            @SuppressWarnings("unchecked")
            Constructor<T> meth = (Constructor<T>) CONSTRUCTOR_CACHE.get(clazz);
            if (meth == null) {
                meth = clazz.getDeclaredConstructor(parameterClasses);
                meth.setAccessible(true);
                CONSTRUCTOR_CACHE.put(clazz, meth);
            }
            result = meth.newInstance(parameters);
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
        return result;
    }
}

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