Java Chapter 4: Loops and Files

Chapter 4: Loops and Files

• This chapter covers loops, input validation, file handling, and generating random numbers in Java.
• Topics include: increment/decrement operators, while loops, do-while loops, for loops, running totals, sentinel values, nested loops, break and continue statements, deciding which loop to use, file input/output, and generating random numbers with the Random class.
• The chapter covers fundamental Java programming concepts related to repetition, data input, and random number generation.

Increment and Decrement Operators

• Java provides shorthand for incrementing (++) and decrementing (--) variables.
• number++ is equivalent to number = number + 1.
• number-- is equivalent to number = number - 1.
• Prefix (++number) and postfix (number++) increment or decrement before or after the expression respectively, making a difference when they appear in expressions.

The while Loop

• A while loop executes a block of code repeatedly as long as a condition is true.
• It's a pretest loop; the condition is checked before each iteration.
• Infinite loops occur when the condition never becomes false.
• Proper use of counters is essential to prevent infinite loops.

The do-while Loop

• A do-while loop is a post-test loop.
• It executes a block of code at least once, then repeatedly checks a condition to determine if an additional iteration should occur.

The for Loop

• A for loop is a pretest loop that is commonly used for iterating a set number of times.
• It combines initialization, condition checking, and increment/decrement steps into a single statement.
• Initialization, test, and update sections can be included, with the test being similar to the while loop. The update is what increments or otherwise changes the counter variable.

Running Totals and Sentinel Values

• Running totals accumulate a sum during iteration, often using a loop.
• Sentinel values signal the end of the input data, typically used when the number of input items isn't known in advance.

Nested Loops

• Nested loops embed one loop inside another.
• The inner loop runs completely for each iteration of the outer loop.

The break Statement

• The break statement prematurely exits a loop.
• It is generally discouraged as it can make code more complex and harder to understand.

The continue Statement

• The continue statement skips the rest of the current loop iteration and moves to the next iteration.

Deciding Which Loop to Use

• Choose between while, do-while, and for loops based on the specific situation.
• while is suitable if the code block may not need to execute at all; do-while if it must run at least once; for if there's a counter or specific number of iterations needing completed.

File Input and Output

• Files are often used to store and retrieve data for re-use.
• Input files are read; output files are written to.
• Two general types of files are binary and text files.
• The file must be closed prior to program termination. Files need to be opened to perform I/O.

The PrintWriter Class

• The PrintWriter class is used for writing data to a text file.
• PrintWriter uses similar methods (print and println) to the System.out.
• The println method adds a newline at the end of the output.

Exceptions

• Exceptions arise when problems occur during a program's execution.
• Methods can either handle the exception or pass it "up the line" to the calling method.
• throws <ExceptionType> clauses specify exceptions that may be raised in a method, indicating that error handling isn't handled in that method.

Generating Random Numbers

• The Random class allows the generation of random numbers within different ranges.

Reading Data From a File

• The File and Scanner classes assist in reading data from a file.
• Scanner offers methods (nextInt, nextLine, etc.) for handling file input like standard input.