Here's a sample of some of the features you'll find in Rephactor topics.

download or run
public class HelloWorld
    public static void main(String[] args)
        System.out.println("Hello, World!");
Run & Revise


interactive elements

Try This:  Color Objects and RGB Values

Adjust the sliders below to see how the RGB values relate to the color:


Color myColor = new Color(183, 44, 150);


Watch This:  Binary Search

quick check
What's this?

Quick Check Scoring

You can answer questions multiple times. Incorrect answers are tracked. For example:

3/6means 3 out of 6 questions in this Quick Check are currently correct
2is the total number of incorrect answers given in this Quick Check

Quick Check

Drag each term to the most appropriate description.

  • semantics
  • natural language
  • debugging
  • syntax error
  • runtime error
  • syntax
  • testing
  • program specification
  • logic error
2169The set of requirements that must be satisfied by a program.
967The meaning of a language element.
1265A problem such as omitting a necessary semicolon.
940The process of determining the root cause of a problem and fixing it.
766The process of evaluating a program to discover errors.
1112A problem such as computing the wrong answer.
679Determines how words and symbols are combined.
1358A problem such as dividing by zero.
1627Used when humans communicate with each other.

common error
API link
key concept
by the way