Java Class New Instance newInstance(String className, Class context)

Description

Instantiates an object using its default constructor if the className is found in the classpath and loaded.

License

Apache License

Declaration

@SuppressWarnings("unchecked")
public static <T> T newInstance(String className, Class<?> context) throws Exception 

Method Source Code

//package com.java2s;
//Licensed under the Apache License, Version 2.0 (the "License");

public class Main {
    /**//from  ww  w.ja  v a2 s .  c o  m
     * Instantiates an object using its default constructor if the {@code className} is 
     * found in the classpath and loaded.
     */
    @SuppressWarnings("unchecked")
    public static <T> T newInstance(String className, Class<?> context) throws Exception {
        Class<T> clazz = (Class<T>) loadClass(className, context, false);
        if (clazz == null)
            throw new Exception(className + " not found in the classpath.");

        return clazz.newInstance();
    }

    /**
     * Instantiates an object using its default constructor if the {@code className} is 
     * found in the classpath and loaded.
     */
    @SuppressWarnings("unchecked")
    public static <T> T newInstance(String className, Class<?> context, boolean checkParent) throws Exception {
        Class<T> clazz = (Class<T>) loadClass(className, context, checkParent);
        if (clazz == null)
            throw new Exception(className + " not found in the classpath.");

        return clazz.newInstance();
    }

    /**
     * Loads a class from the classloader; 
     * If not found, the classloader of the {@code context} class specified will be used.
     */
    public static Class<?> loadClass(String className, Class<?> context) {
        return loadClass(className, context, false);
    }

    /**
     * Loads a class from the classloader; 
     * If not found, the classloader of the {@code context} class specified will be used.
     * If the flag {@code checkParent} is true, the classloader's parent is included in 
     * the lookup.
     */
    public static Class<?> loadClass(String className, Class<?> context, boolean checkParent) {
        Class<?> clazz = null;
        try {
            clazz = Thread.currentThread().getContextClassLoader().loadClass(className);
        } catch (ClassNotFoundException e) {
            if (context != null) {
                ClassLoader loader = context.getClassLoader();
                while (loader != null) {
                    try {
                        clazz = loader.loadClass(className);
                        return clazz;
                    } catch (ClassNotFoundException e1) {
                        loader = checkParent ? loader.getParent() : null;
                    }
                }
            }
        }
        return clazz;
    }
}

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2. newInstance(String className)
3. newInstance(String className)
4. newInstance(String className, Class instanceClazz)
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6. newInstance(String className, Class castTo)
7. newInstance(String className, Class[] parmsCls, Object[] parms)
8. newInstance(String className, Object arg1)
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