cs 5

Chapter 5: Conditionals and Loops

Overview of Conditionals and Loops

• The chapter examines programming statements that allow:

  • Decision making based on conditions

  • Repetition of processing steps in loops

Key Concepts Covered

• Boolean expressions

• If and if-else statements

• Data comparison

• While loops

• Iterators

• ArrayList class

• GUI controls

Flow of Control

• Statement execution is typically linear unless specified otherwise.

• Control structures allow for decision-making and repetition based on boolean expressions.

• Flow of control refers to the order of statement execution in a program.

Conditional Statements

• Conditional statements allow selection of which statement to execute next

• Examples:

  • if statement

  • if-else statement

  • switch statement (explored in Chapter 6)

• These statements enable basic decision-making in Java.

Boolean Expressions

• Conditions typically use Java's comparison operators, returning boolean results:

  • == (equal to)

  • != (not equal to)

  • < (less than)

  • > (greater than)

  • <= (less than or equal to)

  • >= (greater than or equal to)

• Important to distinguish between == and = (assignment operator).

Example of an If Statement

• Syntax:

if (condition) statement;  

• Execution Flow:

  • Condition is evaluated

  • If true, execute statement; if false, skip.

Logical Operators

• Operators for combining boolean expressions:

  • ! (Logical NOT)

  • && (Logical AND)

  • || (Logical OR)

• Each takes boolean operands and returns boolean results.

Logical NOT

• Negates the truth of a condition.

  • If a is true, then !a is false, and vice versa.

Logical AND and OR

• AND (&&) is true if both operands are true.

• OR (||) is true if at least one operand is true.

Short-Circuited Operators

• These operators short-circuit evaluations:

  • If the left operand is sufficient to determine the result, the right operand is not evaluated.

• Example:

if (count != 0 && total/count > MAX) 

• Be cautious with short-circuiting, as it may bypass necessary evaluations.

The If Statement

• Syntax:

if (condition) statement;  

• Indentation is crucial for readability and indicates control structure relationships.

• Reminder: The compiler ignores indentation, leading to potential logical errors.

Example Logic

• Condition evaluated:

  • True: Execute statement.

  • False: Skip.

The If-Else Statement

• Adds an else clause to the if statement:

if (condition) statement1; else statement2;  

• Only one of the statements is executed based on the condition's truth value.

Example Wages.java

• Demonstrates the use of an if-else statement that calculates wages based on hours worked and pays overtime.

Nested If Statements

• An if clause can contain another if statement (nested if).

• The last unmatched if determines which else applies.

Example:

if (num1 < num2)  
    if (num1 < num3) 
        min = num1;  
    else  
        min = num3;  
else if (num2 < num3)  
    min = num2;  
else  
    min = num3;  

Comparing Data

• Important nuances in data types when using boolean expressions.

  • Comparing floating point values for equality requires care to handle precision issues.

  • Special methods and techniques (e.g., Math.abs()) can determine equality for floating-point comparisons.

  • Character and String comparisons rely on Unicode values and appropriate methods (e.g., .equals()).

Example with Floats

• To compare floats:

if (Math.abs(f1 - f2) < TOLERANCE) 
    // Considered equal  

Loops

• Loops are used for repetition in Java.

  • Types of loops include: while, do, and for (discussed in Chapter 6).

The While Statement

• Syntax:

while (condition) statement;  

• Loop runs while the condition is true; evaluates repeatedly until false.

Example of While Loop

• Example demonstrating while loops:

int count = 1;  
while (count <= 5)  
{  
    System.out.println(count);  
    count++;  
}  

Sentinel Values

• Sentinel values signify the end of input for loops.

• Example with sentinel value to compute average input.

Input Validation

• Loops are utilized to ensure valid input, enhancing program robustness.

Infinite Loops

• Fail to change the loop's condition, leading to endless execution.

• Example demonstrating bad logic in loops.

Nested Loops

• Similar to nested if statements, loops can be nested.

Iterators

• Iterators help process collections item by item through methods like .hasNext() and .next().

The ArrayList Class

• Stores lists of objects; capacity adjusts as needed.

• Methods include add(), remove(), get(), and size().

GUI Controls

• Check boxes, radio buttons, and event handlers are essential for user interaction.

Event Handling

• Techniques to manage user actions and update the UI accordingly.

Summary

• Chapter 5 emphasizes understanding boolean expressions, conditional statements, data comparison, loops, iterators, the ArrayList class, and GUI controls.