CODEWITHSUNDEEP
javaclassloader
srk
srk

Reputation: 5136

What are the different ways to load a class in Java

I'm learning java, and in the process of going through the ClassNotFoundException concept, I have come across the term Class.forName("xyz");. I know that this is one way of loading a class. My question is, what are the different ways of loading a class in java? When to use which one? What is preferred over other?

Upvotes: 7

Views: 11670

Answers (1)

AllTooSir
AllTooSir

Reputation: 49372

I will start with the simplest (Here I assume the class definition is available in the classpath and JVM can load it) :

  1. Reference the class name in the code. The class will be loaded latest when the JVM finds that reference.

    SomeClass someInstance = null;

  2. Class.forName(String), to load and initialize the class.It uses classloader of current class.

     Class.forName("XYZ");

  3. ClassLoader#loadClass(String), to load class, but doesn't initialize.You can get an instance of ClassLoader and invoke loadClass() on that instance, which can be a Custom ClassLoader or System ClassLoader.

    ClassLoader.getSystemClassLoader().loadClass("XYZ");

  4. Overloaded Class.forName() , allows you to specify the classloader to use explicitly and initialize parameter to specify whether the class must be initialzed.

    Class.forName(String name, boolean initialize, ClassLoader loader)

For JDBC, we need to load the driver class as well as initialize it. Somewhere the driver class gets registered with the JDBC Driver Manager by running some static initializer(though I haven't seen the inner working code). Hence we need to use a class loading mechanism where the driver class gets loaded and its static initialization blocks run. Hence the most preferred way is Class.forName().

Upvotes: 17

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