ITEC 120 2009spring ibarland nokie jmdymacek

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lect02a
practice with variables

Quick review:

• Types: String ("hello"), int (3), double (3.14).
• Declare a var, then init it:

  int fps; // Number of frames-per-second. fps = 24; // 24 would be movie; 30 would be TV.

• Syntax for calling a method:

  object-dot-methodname-openParen-arguments-closeParen.

  E.g.,

  raki.ufoHeight( 5*fps ) // Assuming 'raki' is a RocketScientist (lect01a) Math.sqrt(24.9) System.out.print( 3+4 );

Suppose we work for Olympic swimming, and want to track the results for an race entrant:

Example: Example: Michael Phelps, in lane 4, swam in 49.27 seconds.

1. Declare a variable which can hold the swimmer's lane-number. (Think about which type to use.) Call your variable it something suggestive (e.g. `frameNum` is better than `q`).
2. Initialize it to a reasonable value.

Today we'll discuss and practice:

• (Book P2.5:) Write a program which swaps the letters 'e' and 'o' in a given string, using the String method replace.
  solution

• Write a program which will print the message:

  Never speak the word "ineffable" again! ...Instead we'll just say "ie".

  Our program will store the forbidden-word (in this case “ineffable”) in a variable. The shortened version consists of the first letter plus the last letter.
  solution

  We'll use the String method charAt to extra individual characters from a String.

  Java trivia: Minor note: We use the escape code \" to embed a quotation-mark in the middle of a string:

  System.out.println( "She says \"hello\" to you." );

  The only other escape code I find myself using often is a newline character, \n. You can see 'advanced tip 4.4' in the book, for more escape codes.

• Your turn: Write a program which prints a word with its last two letters repeated: starting from the word “lecture”, your program prints “lecturere”; starting from the word “class”, your program prints “classss”.

  Java trivia: The java method Character.toString(char) converts individual characters into Strings. For example, Character.toString('m') returns "m".
  (Notice the single-quote vs. double-quote difference between characters and Strings, in Java.)

• Reading input: If you want to prompt the user for an input, you can use the Java method javax.swing.JOptionPane.showInputDialog(String). For example:

  javax.swing.JOptionPane.showInputDialog("What is your quest?")

  Of course, if we want to remember the result of calling that function, we can store it in a variable:

  String job; job = javax.swing.JOptionPane.showInputDialog("What is your quest?");

  Java library trivia: You can use print a message with a corresponding method showMessageDialog. This method requires two inputs, the first of which is always null¹.

  Java trivia: If you want to save some typing, it's possible to write import javax.swing.JOptionPane; at the top of your program. Then, in your program, you can just say JOptionPane and java will know the full-name you are referring to.

  There is nothing mysterious about import — it saves you a bit of typing, that's all.

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©2009, Ian Barland, Radford University Last modified 2009.Jan.30 (Fri)

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