![//********************************************************************
// Age.java Author: Lewis/Loftus
//
// Demonstrates the use of an if statement.
//********************************************************************
import java.util.Scanner;
public class Age
{
//-----------------------------------------------------------------
// Reads the user's age and prints comments accordingly.
//-----------------------------------------------------------------
public static void main(String[] args)
{
final int MINOR = 21;
Scanner scan = new Scanner(System.in);
System.out.print("Enter your age: ");
int age = scan.nextInt();
continue](https://image.slidesharecdn.com/chap05-part2-200316131626/85/Java-Chapter-05-Conditions-Loops-part-2-10-320.jpg)
Java Chapter 05 - Conditions & Loops: part 2
- 1. Chapter 5 Conditionals and Loops: Part 2 • Java Software Solutions • Foundations of Program Design • 9th Edition John Lewis William Loftus
- 2. Key Concept A loop allows a program to execute a statement multiple times.
- 3. Outline Boolean Expressions The if Statement Comparing Data The while Statement Iterators The ArrayList Class
- 4. Key Concept Conditionals and loops allow us to control the flow of execution through a method.
- 5. Flow of Control • Unless specified otherwise, the order of statement execution through a method is linear: one after another • Some programming statements allow us to make decisions and perform repetitions • These decisions are based on boolean expressions (also called conditions) that evaluate to true or false • The order of statement execution is called the flow of control
- 6. Key Concept An if statement allows a program to choose whether to execute a particular statement.
- 7. Conditional Statements • A conditional statement lets us choose which statement will be executed next • They are sometimes called selection statements • Conditional statements give us the power to make basic decisions • The Java conditional statements are the: – if and if-else statement – switch statement • We'll explore the switch statement in Chapter 6
- 8. Boolean Expressions • A condition often uses one of Java's equality operators or relational operators, which all return boolean results: == equal to != not equal to < less than > greater than <= less than or equal to >= greater than or equal to • Note the difference between the equality operator (==) and the assignment operator (=)
- 9. Boolean Expressions • An if statement with its boolean condition: if (sum > MAX) delta = sum – MAX; • First, the condition is evaluated: the value of sum is either greater than the value of MAX, or it is not • If the condition is true, the assignment statement is executed; if it isn't, it is skipped • See Age.java
- 10. //******************************************************************** // Age.java Author: Lewis/Loftus // // Demonstrates the use of an if statement. //******************************************************************** import java.util.Scanner; public class Age { //----------------------------------------------------------------- // Reads the user's age and prints comments accordingly. //----------------------------------------------------------------- public static void main(String[] args) { final int MINOR = 21; Scanner scan = new Scanner(System.in); System.out.print("Enter your age: "); int age = scan.nextInt(); continue
- 11. continue System.out.println("You entered: " + age); if (age < MINOR) System.out.println("Youth is a wonderful thing. Enjoy."); System.out.println("Age is a state of mind."); } }
- 12. continue System.out.println("You entered: " + age); if (age < MINOR) System.out.println("Youth is a wonderful thing. Enjoy."); System.out.println("Age is a state of mind."); } } Sample Run Enter your age: 47 You entered: 47 Age is a state of mind. Another Sample Run Enter your age: 12 You entered: 12 Youth is a wonderful thing. Enjoy. Age is a state of mind.
- 13. Logical Operators • Boolean expressions can also use the following logical operators: ! Logical NOT && Logical AND || Logical OR • They all take boolean operands and produce boolean results • Logical NOT is a unary operator (it operates on one operand) • Logical AND and logical OR are binary operators (each operates on two operands)
- 14. Logical NOT • The logical NOT operation is also called logical negation or logical complement • If some boolean condition a is true, then !a is false; if a is false, then !a is true • Logical expressions can be shown using a truth table: a !a true false false true
- 15. Logical AND and Logical OR • The logical AND expression a && b is true if both a and b are true, and false otherwise • The logical OR expression a || b is true if a or b or both are true, and false otherwise
- 16. Key Concept Logical operators are often used to construct sophisticated conditions.
- 17. Logical AND and Logical OR • A truth table shows all possible true-false combinations of the terms • Since && and || each have two operands, there are four possible combinations of a and b a b a && b a || b true true true true true false false true false true false true false false false false
- 18. Logical Operators • Expressions that use logical operators can form complex conditions if (total < MAX+5 && !found) System.out.println("Proc essing…"); • All logical operators have lower precedence than the relational operators • The ! operator has higher precedence than && and ||
- 19. Boolean Expressions • Specific expressions can be evaluated using truth tables total < MAX found !found total < MAX && !found false false true false false true false false true false true true true true false false
- 20. Short- Circuited Operators • The processing of && and || is “short-circuited” • If the left operand is sufficient to determine the result, the right operand is not evaluated if (count != 0 && total/count > MAX) System.out.println("Te sting."); • This type of processing should be used carefully