CODEWITHSUNDEEP
javaoop
user2268997
user2268997

Reputation: 1391

passing class type as parameter and creating instance of it

I want to pass a class type as a parameter to a method in java.all of which have the same constructor parameter.and create an instance of that Class in that method.is this possible?

Update after some years: do checkout Sapnesh Naik's answer to this, it seems to be the most up-to-date. I have not accepted is as an answer as I do not have a running java stack.
P.S: Give me a shout if you can verify.

Upvotes: 22

Views: 41934

Answers (5)

Sapnesh Naik
Sapnesh Naik

Reputation: 11656

newInstance() is Deprecated.

This method propagates any exception thrown by the nullary constructor, including a checked exception. Use of this method effectively bypasses the compile-time exception checking that would otherwise be performed by the compiler. The Constructor.newInstance method avoids this problem by wrapping any exception thrown by the constructor in a (checked) java.lang.reflect.InvocationTargetException.

The deprecated call:

clazz.newInstance()

Can be replaced by:

clazz.getDeclaredConstructor().newInstance()

Example:

void MyMethod(Class type) throws InstantiationException, IllegalAccessException {
    type.getDeclaredConstructor().newInstance();
}

Upvotes: 7

drew moore
drew moore

Reputation: 32680

You're looking for Reflection.

Your method would look something like this: 

public void m1(Class c) {

      try {
        Object obj = c.newInstance();
        //do something with your new instance
    } catch (InstantiationException ex) {

    } catch (IllegalAccessException ex) {

    }
}

The Oracle doc for the Reflection API is here

Upvotes: 3

Evgeniy Dorofeev
Evgeniy Dorofeev

Reputation: 136072

Yes you can

void x(Class cls) throws InstantiationException, IllegalAccessException {
    cls.newInstance();
}

Note that Class.newInstance may fail with

IllegalAccessException - if the class or its nullary constructor is not accessible.

InstantiationException - if this Class represents an abstract class, an interface, an array class, a primitive type, or void; or if the class has no nullary constructor; or if the instantiation fails for some other reason.

see API for more

Upvotes: 1

Narendra Pathai
Narendra Pathai

Reputation: 41975

Using reflection to create the instance:

Object obj = clazz.newInstance();

This will use the default no-arg constructor to create the instance.

Constructor<?> constructor = clazz.getConstructor(String.class);
Object object = constructor.newInstance(new Object[] { strArgument });

To create the instance if you have some other constructor which takes arguments.

Upvotes: 19

Petar Ivanov
Petar Ivanov

Reputation: 93060

You need to use reflection to do that, but yeah it is certainly possible.

void MyMethod(Class className)
{
    try {
        Object obj = className.newInstance();
        //obj is a newly created object of the passed in type
    }
    catch (Exception ex) { }
}

Upvotes: 4

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