CS 1063 Week 1:  Introduction to Computer Programming

Objectives

• Administrative
• Use the web to obtain class notes, assignments, projects, and calendar dates
• Type in a simple program in DrJava and execute it

Administrative

• Syllabus
• Fill out survey
• DrJava software
• Course mechanics
• Labs  (10)
• Quizzes  (10)
• Projects  (3)
• Tests  (2 and a final)
• Course web page
• http://www.cs.utsa.edu/~cs1063

Activity 1:  Compiling a Simple Program

Instructions for DrJava can be found at http://www.cs.utsa.edu/~cs1063/resources/gettingstarteddrjava.html

Part 1:  Setup - Find DrJava on your computer and execute it.

• Create a new class called HelloWorld by typing the following in the Definitions pane.

  public class HelloWorld {
    public static void main(String[] args) {
      System.out.println("Hello World!");
    }
  }
  

• Java is case-sensitive.  You must enter upper and lowercase letters exactly as they appear in the program listing.
• Save the class.
• Compile the class.
• Run the class.  You should see Hello World! in the Console pane.

• Every Java application contains a class with a main method.  When the application starts, the instructions in the main method are executed.

  public static void main(String[] args) {
      .    .    .
  }
  

• Use comments to help human readers understand your program.  Add the following line to your program.
  

  public class HelloWorld {
    public static void main(String[] args) {
      // display a greeting in the console pane
      System.out.println("Hello World!");
    }
  }
  

  • Any text enclosed between // and the end of the line is completely ignored by the compiler.
  • Comments are used to explain the program to other programmers or to yourself.
  • The compiler also ignores any text between a /* and */  If you have a comment that is longer than one line then the /* . . . */ comment is simpler.  For example:

  
  /* This is a simple Java program
     It will print a greeting to the console
  */
  

• Add the highlighted lines to your HelloWorld file and run again.  Was there any change?
  
• Instructions or statements in the body of the main method (statements between {} ) are executed one at a time.  Each statement ends in a semicolon (;).
  • Notice that our main has only one statement - System.out.println("Hello World!");
  • The comment is ignored.
• Whenever you call a method in Java, you need to specify three things
• The object that you want to use - System.out
• The name of the method you want to use - println
• A pair of parentheses, containing any other information (parameters) needed by the method -
  ("Hello World!")

• String - a sequence of characters enclosed in quotation marks.
• The println method prints a string or a number and then starts a new line.  The following code prints out the two lines

  Hello
  World!
  

  
  System.out.println("Hello");
  System.out.println("World!");