An anonymous class is a special type of class in Java that does not have a name. It is often used for creating one-time objects or for implementing interfaces in a more concise way. However, one of the limitations of anonymous classes is that they do not have constructors that can be accessed from outside the class. In this article, we will explore how to access the constructor of an anonymous class and why it is useful.
First, let's understand why anonymous classes do not have constructors that can be accessed from outside. This is because the constructor for an anonymous class is implicitly created by the compiler and is not visible in the code. It is also not possible to define a constructor for an anonymous class explicitly. This is why it is not possible to access the constructor of an anonymous class using the traditional way of using the "new" keyword.
However, there are certain scenarios where we might want to access the constructor of an anonymous class. For example, if we want to pass parameters to the constructor or if we want to create multiple instances of the anonymous class. In such cases, we need to find an alternative way to access the constructor.
The solution to this problem is to use an instance initializer block. This is a block of code that is executed when an instance of the anonymous class is created. It is similar to a constructor, but it is not actually a constructor. This block of code is executed after the implicit constructor of the anonymous class is called. So, by using this block, we can effectively access the constructor of an anonymous class.
Let's see an example of how to use an instance initializer block to access the constructor of an anonymous class.
```
interface Greeting {
void sayHello();
}
public class AnonymousClassExample {
public static void main(String[] args) {
Greeting greeting = new Greeting() {
// instance initializer block
{
System.out.println("Executing instance initializer block");
}
// overridden method
@Override
public void sayHello() {
System.out.println("Hello from anonymous class");
}
};
greeting.sayHello();
}
}
```
In the above example, we have created an anonymous class that implements the Greeting interface. Inside the instance initializer block, we have printed a message to show that it is being executed. Then, the overridden method sayHello() is called from the main method. When we run this code, the output will be:
```
Executing instance initializer block
Hello from anonymous class
```
As you can see, the instance initializer block is executed before the overridden method is called. This shows that we have successfully accessed the constructor of the anonymous class.
Now, let's see another example where we pass parameters to the constructor of an anonymous class using the instance initializer block.
