Instantiate a class by name stores in String in Java

For beginners like me that are not very familiar with object oriented concepts, it might be impossible to imagine that Java has a capability to instantiate a class by its name stored in a string variable. However, this is totally possible in Java or even in other programming languages with utilizing reflector/reflection concept.

Take a look at below example,

public class A {
    private int x;

    public void setX(int x) {
        this.x = x;
    }

    public int getX() {
        return this.x;
    }
}

Now the objective is to create an instance of class A which its name stored in variable, this code does that.

public class Test {
    public void main(String[] args) {
        String className = "A";
        Class myClass = Class.forName(className);
        //Now need to make an object
        // This is a general Object type, must convert to call method.
        Object obj = myClass.newInstance(); 
        A aClass = (A) obj;
        //Shorter way
        A aClass = (A) Class.forName(className).newInstance();
    }
}

Now it might be a question what the reflection is used for, the answer is so simple, one practical example is making database connection.

You can refer to the following links for DB connection.

Resources

• Official Oracle website
• Tutorialspoint website
• Stackoveflow