Java Class New Instance newInstance(String className, Object... params)

Description

Creates a new instance.

License

Mozilla Public License

Parameter

Parameter	Description
className	a string with the entire class, eg. "java.lang.Integer"
params	the constructor parameters

Return

the newly created object

Declaration

public static Object newInstance(String className, Object... params) throws Exception 

Method Source Code

//package com.java2s;
/*/*from w w w  .ja  v  a2 s  . c  o m*/
 * Copyright 2004-2014 H2 Group. Multiple-Licensed under the MPL 2.0,
 * and the EPL 1.0 (http://h2database.com/html/license.html).
 * Initial Developer: H2 Group
 */

import java.lang.reflect.Constructor;

public class Main {
    /**
     * Creates a new instance. This will try to use the constructor where the
     * most parameter classes match exactly (this algorithm is simpler than the
     * one in the Java specification, but works well for most cases).
     *
     * @param className a string with the entire class, eg. "java.lang.Integer"
     * @param params the constructor parameters
     * @return the newly created object
     */
    public static Object newInstance(String className, Object... params) throws Exception {
        Constructor<?> best = null;
        int bestMatch = 0;
        for (Constructor<?> c : Class.forName(className).getConstructors()) {
            int p = match(c.getParameterTypes(), params);
            if (p > bestMatch) {
                bestMatch = p;
                best = c;
            }
        }
        if (best == null) {
            throw new NoSuchMethodException(className);
        }
        return best.newInstance(params);
    }

    private static int match(Class<?>[] params, Object[] values) {
        int len = params.length;
        if (len == values.length) {
            int points = 1;
            for (int i = 0; i < len; i++) {
                Class<?> pc = getNonPrimitiveClass(params[i]);
                Object v = values[i];
                Class<?> vc = v == null ? null : v.getClass();
                if (pc == vc) {
                    points++;
                } else if (vc == null) {
                    // can't verify
                } else if (!pc.isAssignableFrom(vc)) {
                    return 0;
                }
            }
            return points;
        }
        return 0;
    }

    /**
     * Convert primitive class names to java.lang.* class names.
     *
     * @param clazz the class (for example: int)
     * @return the non-primitive class (for example: java.lang.Integer)
     */
    public static Class<?> getNonPrimitiveClass(Class<?> clazz) {
        if (!clazz.isPrimitive()) {
            return clazz;
        } else if (clazz == boolean.class) {
            return Boolean.class;
        } else if (clazz == byte.class) {
            return Byte.class;
        } else if (clazz == char.class) {
            return Character.class;
        } else if (clazz == double.class) {
            return Double.class;
        } else if (clazz == float.class) {
            return Float.class;
        } else if (clazz == int.class) {
            return Integer.class;
        } else if (clazz == long.class) {
            return Long.class;
        } else if (clazz == short.class) {
            return Short.class;
        } else if (clazz == void.class) {
            return Void.class;
        }
        return clazz;
    }
}

Related

1. newInstance(String className, Class[] parmsCls, Object[] parms)
2. newInstance(String className, Object arg1)
3. newInstance(String className, Object... args)
4. newInstance(String className, Object... args)
5. newInstance(String className, Object... parameters)
6. newInstance(String className, Object[] args)
7. newInstance(String className, Object[] args)
8. newInstance(String className, Object[] args)
9. newInstance(String classname, Properties properties)