Java Class New Instance newInstance(String className)

Description

new Instance

License

Apache License

Declaration

@SuppressWarnings("unchecked")
    public static <T> T newInstance(String className)
            throws ClassNotFoundException 

Method Source Code

//package com.java2s;
/**//from   w  w  w.  java 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.Map;
import java.util.concurrent.ConcurrentHashMap;

import com.google.common.base.Preconditions;

public class Main {
    private static final Map<Class<?>, Constructor<?>> CONSTRUCTOR_CACHE = new ConcurrentHashMap<Class<?>, Constructor<?>>();

    @SuppressWarnings("unchecked")
    public static <T> T newInstance(String className)
            throws ClassNotFoundException {
        return newInstance((Class<T>) Class.forName(className));
    }

    @SuppressWarnings("unchecked")
    public static <T> T newInstance(Class<T> theClass) {
        Preconditions.checkNotNull(theClass);
        T result;
        try {
            Constructor<T> meth = (Constructor<T>) CONSTRUCTOR_CACHE
                    .get(theClass);
            if (null == meth) {
                meth = theClass.getDeclaredConstructor(new Class[0]);
                meth.setAccessible(true);
                CONSTRUCTOR_CACHE.put(theClass, meth);
            }
            result = meth.newInstance();
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
        return result;
    }

    /**
     * Create an instance using class literal name and object values supplied.
     * 
     * @param className is the string name of the class to be created.
     * @param values supplied in object array.
     * @exception ClassNotFoundException
     */
    @SuppressWarnings("unchecked")
    public static <T> T newInstance(String className, Object[] values)
            throws ClassNotFoundException {
        return newInstance((Class<T>) Class.forName(className), values);
    }

    /**
     * Create an instance with corresponded class and object values supplied.
     * Constructor
     * 
     * @param theClass supplies instance to be created.
     * @param values are parameters applied when instance is created.
     */
    @SuppressWarnings({ "unchecked", "rawtypes" })
    public static <T> T newInstance(Class<T> theClass, Object[] values) {
        T result;
        try {
            Constructor<T> meth = (Constructor<T>) CONSTRUCTOR_CACHE
                    .get(theClass);
            if (null == meth) {
                Class[] parameters = new Class[values.length];
                int idx = 0;
                for (Object value : values) {
                    parameters[idx++] = value.getClass();
                }
                meth = theClass.getDeclaredConstructor(parameters);
                meth.setAccessible(true);
                CONSTRUCTOR_CACHE.put(theClass, meth);
            }
            result = meth.newInstance(values);
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
        return result;

    }

    /**
     * Create an instance with corresponded class and object values supplied.
     * Constructor
     * 
     * @param theClass supplies instance to be created.
     * @param parameters are class type of object values supplied.
     * @param values are parameters applied when instance is created.
     */
    @SuppressWarnings({ "unchecked", "rawtypes" })
    public static <T> T newInstance(Class<T> theClass, Class[] parameters,
            Object[] values) {
        T result;
        try {
            Constructor<T> meth = (Constructor<T>) CONSTRUCTOR_CACHE
                    .get(theClass);
            if (null == meth) {
                meth = theClass.getDeclaredConstructor(parameters);
                meth.setAccessible(true);
                CONSTRUCTOR_CACHE.put(theClass, meth);
            }
            result = meth.newInstance(values);
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
        return result;
    }
}

Related

1. newInstance(String className)
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9. newInstance(String className, Class cls)