Java Class New Instance newInstance(Class theClass)

Description

Construct a class

License

Apache License

Parameter

Parameter	Description
T	template type
theClass	a parameter

Return

the instance

Declaration

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

Method Source Code

//package com.java2s;
/*******************************************************************************
 * Copyright 2012 Internet2/*  w w w . jav  a  2  s . c  om*/
 * 
 * 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.lang.reflect.Modifier;

public class Main {
    /**
     * Construct a class
     * @param <T> template type
     * @param theClass
     * @return the instance
     */
    public static <T> T newInstance(Class<T> theClass) {
        try {
            return theClass.newInstance();
        } catch (Throwable e) {
            if (theClass != null
                    && Modifier.isAbstract(theClass.getModifiers())) {
                throw new RuntimeException("Problem with class: "
                        + theClass + ", maybe because it is abstract!", e);
            }
            throw new RuntimeException("Problem with class: " + theClass, e);
        }
    }

    /**
     * Construct a class
     * @param <T> template type
     * @param theClass
     * @param allowPrivateConstructor true if should allow private constructors
     * @return the instance
     */
    public static <T> T newInstance(Class<T> theClass,
            boolean allowPrivateConstructor) {
        if (!allowPrivateConstructor) {
            return newInstance(theClass);
        }
        try {
            Constructor<?>[] constructorArray = theClass
                    .getDeclaredConstructors();
            for (Constructor<?> constructor : constructorArray) {
                if (constructor.getGenericParameterTypes().length == 0) {
                    if (allowPrivateConstructor) {
                        constructor.setAccessible(true);
                    }
                    return (T) constructor.newInstance();
                }
            }
            //why cant we find a constructor???
            throw new RuntimeException(
                    "Why cant we find a constructor for class: " + theClass);
        } catch (Throwable e) {
            if (theClass != null
                    && Modifier.isAbstract(theClass.getModifiers())) {
                throw new RuntimeException("Problem with class: "
                        + theClass + ", maybe because it is abstract!", e);
            }
            throw new RuntimeException("Problem with class: " + theClass, e);
        }
    }
}

Related

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