Java Class New Instance newInstance(Class type)

Description

A helper method to create a new instance of a type using the default constructor arguments.

License

Apache License

Exception

Parameter	Description
IllegalAccessException	an exception
InstantiationException	an exception

Declaration

public static <T> T newInstance(Class<T> type) throws InstantiationException, IllegalAccessException 

Method Source Code

//package com.java2s;
//License from project: Apache License 

public class Main {
    /**//from   w w w.  ja v  a 2 s . co  m
     * A helper method to create a new instance of a type using the default
     * constructor arguments.
     * @throws IllegalAccessException 
     * @throws InstantiationException 
     */
    public static <T> T newInstance(Class<T> type) throws InstantiationException, IllegalAccessException {

        return type.newInstance();

    }

    /**
     * A helper method to create a new instance of a type using the default
     * constructor arguments.
     * @throws IllegalAccessException 
     * @throws InstantiationException 
     */
    public static <T> T newInstance(Class<?> actualType, Class<T> expectedType)
            throws InstantiationException, IllegalAccessException {

        Object value = actualType.newInstance();
        return cast(expectedType, value);

    }

    /**
     * Converts the given value to the required type or throw a meaningful exception
     */
    @SuppressWarnings("unchecked")
    public static <T> T cast(Class<T> toType, Object value) {
        if (toType == boolean.class) {
            return (T) cast(Boolean.class, value);
        } else if (toType.isPrimitive()) {
            Class newType = convertPrimitiveTypeToWrapperType(toType);
            if (newType != toType) {
                return (T) cast(newType, value);
            }
        }
        try {
            return toType.cast(value);
        } catch (ClassCastException e) {
            throw new IllegalArgumentException(
                    "Failed to convert: " + value + " to type: " + toType.getName() + " due to: " + e, e);
        }
    }

    /**
     * Converts primitive types such as int to its wrapper type like
     * {@link Integer}
     */
    public static Class<?> convertPrimitiveTypeToWrapperType(Class<?> type) {
        Class<?> rc = type;
        if (type.isPrimitive()) {
            if (type == int.class) {
                rc = Integer.class;
            } else if (type == long.class) {
                rc = Long.class;
            } else if (type == double.class) {
                rc = Double.class;
            } else if (type == float.class) {
                rc = Float.class;
            } else if (type == short.class) {
                rc = Short.class;
            } else if (type == byte.class) {
                rc = Byte.class;
            } else if (type == boolean.class) {
                rc = Boolean.class;
            }
        }
        return rc;
    }
}

Related

1. newInstance(Class type)
2. newInstance(Class type)
3. newInstance(Class type)
4. newInstance(Class type)
5. newInstance(Class type)
6. newInstance(Class type, Class declarator, Annotation annotation)
7. newInstance(Class type, Class[] parameterTypes, Object[] args)
8. newInstance(Class type, Object... args)
9. newInstance(Class type, Object... params)