While calling a constructor from another constructor in a class using this keyword, the call should be

When calling one constructor from another constructor in the same class using the this keyword, the call should be made as the first statement in the constructor. This is known as constructor chaining.

Here's a breakdown of how this works:

1. Constructor Call: Use this(parameters) to call another constructor of the same class. This allows you to initialize fields in one constructor and then call another constructor to reduce redundancy in the code.

2. Syntax: The syntax looks like this:

   public ClassName(parameters) {
       this(parameters); // Calls another constructor
       // additional code
   }
   

3. First Statement Rule: The this call must be the first statement in the constructor. If any other statement appears before it, the code will result in a compile-time error.

Example:

public class Example {
    private int value;

    // First constructor
    public Example(int val) {
        this.value = val; // Initialize value
    }

    // Second constructor
    public Example() {
        this(10); // Calls the first constructor with a default value
    }
}

In the example above, when an instance of Example is created with no parameters, it defaults to calling the first constructor with a value of 10, demonstrating proper usage of constructor chaining with the this keyword.