Lesson 4: Decision Control Structures

Lesson Overview & Midterm Context

• Instructor: JHON RENZ BRYAN DELA FUENTE
• Lesson Title: Lesson 4. Decision Control Structures
• Midterm Examination Notice: Lesson 4 is explicitly included in the Midterm Examination. Due to class cancellation, this lesson is assigned for self-study using the designated web resources.
• Core Topics:
  • Topic 1: Conditional Structures
  • Topic 2: Decision-making in program design
• Assigned Reference Links:
  • https://www.w3schools.com/java/java_conditions.asp
  • https://www.w3schools.com/java/java_conditions_else.asp
  • https://www.w3schools.com/java/java_conditions_elseif.asp
  • https://www.w3schools.com/java/java_conditions_shorthand.asp
  • https://www.w3schools.com/java/java_conditions_nested.asp
  • https://www.w3schools.com/java/java_conditions_logical.asp
  • https://www.w3schools.com/java/java_switch.asp

Topic 1: Conditional Structures & Java If Statements

• Mathematical Logical Operators: Java conditions leverage standard mathematical comparisons that return a boolean value (true or false):
  • Less than: a < b
  • Less than or equal to: a <= b
  • Greater than: a > b
  • Greater than or equal to: a >= b
  • Equal to: a == b
  • Not Equal to: a != b
• The if Statement:
  • Used to specify a block of Java code to be executed only if a given condition evaluates to true.
  • Syntax: java if (condition) { // block of code to be executed if the condition is true }     
  • Syntax Casing Rule: Java keywords are strictly case-sensitive. The keyword if must be written in lowercase; using IF or If generates a compiler error.

The else and else if Branching Statements

• The else Statement:
  • Used to specify a alternative block of code to be executed if the if condition evaluates to false.
  • Syntax: java if (condition) { // block of code to be executed if condition is true } else { // block of code to be executed if condition is false }     
• The else if Statement:
  • Used to specify a new condition to test if the preceding condition evaluates to false.
  • Syntax: java if (condition1) { // block executed if condition1 is true } else if (condition2) { // block executed if condition1 is false and condition2 is true } else { // block executed if both condition1 and condition2 are false }     
• Sequential Execution: The program tests conditions in top-down order. The moment a condition evaluates to true, its corresponding code block is executed and all subsequent branches in the block are bypassed.

Short Hand If…Else (Ternary Operator)

• Definition: The ternary operator provides a concise, single-line mechanism for conditional evaluation and variable assignment.
• Syntax Structure:
  • variable = (condition) ? expressionTrue : expressionFalse;
• Component Breakdown:
  • condition: A boolean expression tested by the operator.
  • ?: Symbol separating the tested condition from the true outcome expression.
  • expressionTrue: Evaluated and returned if the condition is true.
  • :: Symbol separating the true expression from the false outcome expression.
  • expressionFalse: Evaluated and returned if the condition is false.

Topic 2: Decision-Making in Program Design

• Nested Conditional Structures:
  • Involves placing an if or else if statement inside another if or else block.
  • Used when dependent decisions require a primary pre-requisite condition to evaluate to true before checking subordinate conditions.
  • Syntax: java if (condition1) { // Executes if condition1 is true if (condition2) { // Executes only if both condition1 and condition2 are true } }     
• Logical Operators in Decision Control:
  • Used to combine multiple boolean conditions or invert logical states within conditional control statements.
  • Logical AND (&&): Returns true only if both conditions/statements evaluate to true.
  • Logical OR (||): Returns true if at least one of the conditions/statements evaluates to true.
  • Logical NOT (!): Inverts the logical result; returns false if the statement is true, and true if it is false.

Multi-Way Decision Structures: The Java Switch Statement

• Purpose: Used to select one of many distinct code blocks to execute based on exact matching of an expression value, serving as a structured alternative to multi-branch if...else if chains.
• Syntax Structure: java switch(expression) { case x: // code block break; case y: // code block break; default: // code block }   
• Key Control Keywords:
  • switch: Evaluates an expression once and compares its resulting value against each case label.
  • case: Defines a candidate target value to match against the switch expression.
  • break: Halts execution and exits the switch block upon execution. Without a break statement, execution falls through into subsequent case blocks regardless of whether their condition matches.
  • default: Optional clause executed if none of the defined case values match the evaluated expression.