Building Java Programs Chapter 1 - PowerPoint PPT Presentation

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Building Java Programs Chapter 1

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  1. Building Java ProgramsChapter 1 Errors

  2. Objectives • Recognize different errors that Java uses and how to fix them.

  3. 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

  4. Syntax error example • Where are the errors in the following program? 1public class Hello { 2pooblic static void main(String[] args) { 3System.owt.println("Hello, world!") 4 } 5 } Compiler output: Hello.java:2: <identifier> 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!

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

  6. Runtime error example • Where are the errors in the following program? 1public 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!

  7. 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 JGraspto 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