BUILDING JAVA PROGRAMSCHAPTER 1ERRORS

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OBJECTIVES

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

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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

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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: <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!

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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!

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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!

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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