Java Class New Instance newInstance(Class theClass)

Description

Create an object of the given class using a no-args constructor

License

Apache License

Parameter

Parameter	Description
theClass	class to return new object of
T	the type of the class to be returned

Return

an object of the requested type

Declaration

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

Method Source Code

//package com.java2s;
/*//from www . ja v  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
 * <p>
 * http://www.apache.org/licenses/LICENSE-2.0
 * <p>
 * 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 {
    /**
     * Create an object of the given class.
     * @param theClass
     * @param parameterTypes
     *          an array of parameterTypes for the constructor
     * @param initargs
     *          the list of arguments for the constructor
     */
    public static <T> T newInstance(Class<T> theClass, Class<?>[] parameterTypes, Object[] initargs) {
        // Perform some sanity checks on the arguments.
        if (parameterTypes.length != initargs.length) {
            throw new IllegalArgumentException(
                    "Number of constructor parameter types doesn't match number of arguments");
        }
        for (int i = 0; i < parameterTypes.length; i++) {
            Class<?> clazz = parameterTypes[i];
            if (initargs[i] != null && !(clazz.isInstance(initargs[i]))) {
                throw new IllegalArgumentException("Object : " + initargs[i] + " is not an instance of " + clazz);
            }
        }

        try {
            Constructor<T> meth = theClass.getDeclaredConstructor(parameterTypes);
            meth.setAccessible(true);
            return meth.newInstance(initargs);
        } catch (Exception e) {
            throw new RuntimeException("Unable to instantiate " + theClass.getName(), e);
        }
    }

    /**
     * Create an object of the given class using a no-args constructor
     * @param theClass class to return new object of
     * @param <T> the type of the class to be returned
     * @return an object of the requested type
     */
    public static <T> T newInstance(Class<T> theClass) {
        try {
            return theClass.newInstance();
        } catch (InstantiationException | IllegalAccessException e) {
            throw new RuntimeException("Unable to instantiate " + theClass.getName(), e);
        }
    }
}

Related

1. newInstance(Class klass, Object... args)
2. newInstance(Class listener)
3. newInstance(Class sourceClass)
4. newInstance(Class targetType, String className, ClassLoader loader)
5. newInstance(Class tClass, Object... initargs)
6. newInstance(Class theClass)
7. newInstance(Class theClass)
8. newInstance(Class theClass, Class[] parameterTypes, Object[] initargs)
9. newInstance(Class theClass, Object... initArgs)