Java Class New Instance newInstance(Class clazz)

Description

Create an object for the given class using its default constructor.

License

Apache License

Declaration

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

Method Source Code

//package com.java2s;
/**/*from   w w w  .jav  a 2  s .  c o m*/
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.*;
import java.util.concurrent.ConcurrentHashMap;

public class Main {
    public static final Class<?>[] EMPTY_CLASSES = {};
    /**
     * Cache of constructors for each class. Pins the classes so they
     * can't be garbage collected until ReflectionUtils can be collected.
     */
    private static final Map<List<Class<?>>, Constructor<?>> CONSTRUCTOR_CACHE = new ConcurrentHashMap<>();

    /**
     * Create an object for the given class using its default constructor.
     */
    public static <T> T newInstance(Class<T> clazz) {
        return newInstance(clazz, EMPTY_CLASSES);
    }

    /**
     * Create an object for the given class using the specified constructor.
     *
     * @param clazz class of which an object is created
     * @param argClasses argument classes of the constructor
     * @param args actual arguments to be passed to the constructor
     * @param <T> class type of clazz
     * @return a new object
     */
    public static <T> T newInstance(Class<T> clazz, Class<?>[] argClasses,
            Object... args) {
        Objects.requireNonNull(clazz, "clazz == null");
        try {
            final List<Class<?>> key = new ArrayList<>();
            key.add(clazz);
            key.addAll(Arrays.asList(argClasses));

            @SuppressWarnings("unchecked")
            Constructor<T> ctor = (Constructor<T>) CONSTRUCTOR_CACHE
                    .get(key);
            if (ctor == null) {
                ctor = clazz.getDeclaredConstructor(argClasses);
                ctor.setAccessible(true);
                CONSTRUCTOR_CACHE.put(key, ctor);
            }
            return ctor.newInstance(args);
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }
}

Related

1. newInstance(Class clazz)
2. newInstance(Class clazz)
3. newInstance(Class clazz)
4. newInstance(Class clazz)
5. newInstance(Class clazz)
6. newInstance(Class clazz)
7. newInstance(Class clazz, Class[] argumentTypes, Object[] arguments)
8. newInstance(Class clazz, Class[] parameterTypes, Object[] initargs)
9. newInstance(Class cls)