CS1112 > From Matlab to Java

If you will learn Java next, read Appendix C "Matlab, Java, and C" in our textbook Insight. Below are the "Java translations" of some of the Matlab examples from the course to get you oriented.

Project 2 Problem 1: Matlab script to Java program

The Java code, also called the source code, is in the file CubeRoot.java, i.e., the class name is "CubeRoot". The code to be executed is contained in a method called "main". A Java method corresponds to a Matlab function. So a single Matlab script (in this case cubeRoot.m) translates to a java program with one class file (in this case CubeRoot.java) that contains one method called main. To execute the Java program is to compile the file CubeRoot.java and execute its main method. Other differences to observe:
  1. Each variable must be declared: its type explicitly specified.
  2. The semicolon indicates the end of a statement; it is not for suppressing output.
  3. Simple printing with no format specification is typically done using the method println or print from class out in package System. The System package is automatically available--no need to import.
  4. Braces, { }, are used to enclose a block of Java code instead of the keyword end in Matlab. See the while-loop, the main method block, and the class block for example.
  5. Common arithmetic built-in functions are in the Math class. E.g, Math.pow(x,y) in Java is x^y in Matlab.
  6. A single-line comment is preceded by //; a multi-line comment block is enclosed with /* and */ like this:
    /* comment line 1
       comment line 2

Project 2 Problem 1 modified: Matlab function to Java static method

cubeRoot.m as above → CubeRootVariation.java
A cube root function, called myCubeRoot, is implemented to return the estimated cube root. In the class CubeRootVariation, method myCubeRoot computes and returns the cube root while method main contains the code that calls method myCubeRoot several times with various arguments. These methods are static methods--methods that can be called without an object of the class. The code in this file, as well as that in CubeRoot.java of the previous example, is non-object-oriented. Other differences to observe:
  1. The type of each parameter in the method header must be specified.
  2. Each method has a return type. Method myCubeRoot has the return type double in the method header; therefore it ends with a return statement that returns a value of type double. Method main has the return type void in the method header, meaning that it does not return anything; therefore method main does not have a return statement. A method in Java may return only one thing.
  3. The for-loop syntax is quite different from that in Matlab.

Project 6 stained glass image: OOP

The object-oriented concepts used are the same between Matlab and Java! The differences you see are mainly due to syntax and the setup necessary in Java for producing graphics and reading an image. The same OO design involving three classes is used: StainedGlassImage, Tile, and Vertex. Observe these differences:
  1. In an instance method, there is not a parameter that refers to the instance itself. This is in contrast to the self-reference parameter (that we often named self) that is always the first parameter of a Matlab instance method. In Java, there is an implicit reference this, which refers to the instance itself. See instance method perturb in class Vertex for example. The method header does not include a parameter to the object itself; yet inside the method you see the keyword this used to reference the object itself.
  2. In class Tile, the package awt is imported for doing graphics in the instance method draw.
  3. In class StainedGlassImage, several packages are imported to handle graphics (drawing and painting), the window for displaying graphics (JPanel), and jpeg image files.
  4. To instantiate an object, the keyword new is used in addition to calling the constructor.
  5. In class StainedGlassImage, we implement an instance method imread to do what Matlab's built-in imread does.
  6. In class StainedGlassImage, the main method contains the code to be executed in order to instantiate the StainedGlassImage object, i.e., to produce the stained glass image graphics. Notice that the main method is static, i.e., an object is not necessary in order to call main; this has to be true since main is the starting point of a Java program.