BUILDING JAVA PROGRAMS CHAPTER 1 ERRORS

22 OBJECTIVES Recognize different errors that Java uses and how to fix them.

33 LET’S GET STARTED When you write programs, there are three types of errors that you may introduce… what are they? Syntax Errors Logic Errors Runtime Errors

44 SYNTAX ERROR EXAMPLE Where are the errors in the following program? 1 public class Hello { 2 pooblic static void main(String[] args) { 3 System.owt.println("Hello, world!") 4 } 5 } Compiler output: Hello.java:2: expected pooblic static void main(String[] args) { ^ Hello.java:3: ';' expected } ^ 2 errors The compiler shows the line number where it found the error. The error messages can be tough to understand!

55 LOGIC ERROR EXAMPLE Where are the errors in the following program? 1 public class Hello { 2 public static void main(String[] args) { 3 System.out.println("Hello, “ 4 + “world!"); 5 } 6 } Compiler output? Nothing! Only the programmer can catch logic errors. Program output? Unexpected: Hello, World!

66 RUNTIME ERROR EXAMPLE Where are the errors in the following program? 1 public class Hello { 2 public static void main(String[] args) { 3 Function1DividedBy0(); 4 } 5 } Compiler output? Nothing. (Unless you have a smart compiler!) Program output? Crash!

77 WITH A PARTNER (OR TWO) Divide your notebook into three sections: Syntax, Logic, and Runtime. For each section, see how many different types of errors you can come up with. You can use JGrasp to help you think of errors. Hint: Start from a working version of the Hello.java program. Here are some examples to get you started Syntax: Missing a semicolon Logic: Calling the wrong function Runtime: Dividing by 0