Unit 3 Selections
Github Code
Learning
- Making the computer seem smart with IF and IF-ELSE selection statements based on Boolean variables and expressions.
- Using Switch-Case.
- Creating Random numbers.
- Formatting output
The boolean Type and Operators
- Often in a program you need to compare two values, such as whether i is greater than j.
- Java provides six comparison operators (also known as relational operators) that can be used to compare two values.
- The result of the comparison is a Boolean value: true or false.
- boolean 1 Bit => Range= true/false
public class Main {
public static void main(String[] args) {
boolean b = (1 > 2);
System.out.println(b);
if(true){
System.out.println("Welcome to IS147");
}
}
}
Boolean Example
Sample code on Github boolean code
Comparison Operators
If Statements
//boolean expression returns true or false
if (boolean-expression) {
statement(s);
}
int radius=5;
if (radius >= 0) {
area = radius * radius * PI;
System.out.println("The area"
+ " for the circle of radius "
+ radius + " is " + area);
}
Example of if
public class Main {
public static void main(String[] args) {
int x = 20;
int y = 18;
if (x > y) {
System.out.println("x is greater than y");
}
}
}
If Condition
Note
The if/else Statement
public class Ifelse {
int number = 4;
public static void main(String[] args) {
if (boolean-expression) {
statement(s)-for-the-true-case;
}
else {
statement(s)-for-the-false-case;
}
}
}
if-else Example
Sample code on Github if else code
public class Main{
public static void main(String[] args) {
int radius = 0;
double area;
if (radius > 0) {
area = radius * radius * 3.14159;
System.out.println("The area for the"
+ "circle of radius " + radius +
" is " + area);
}
else {
System.out.println("Negative input");
}
}
}
IF else video
Multiple Alternative if Statements
Multi-Way if-else Statements
Trace if-else statement
Trace if else via code
Github codeChallenge #1
Github codeThe else clause matches the most recent if clause in the same block.
Challenge #2
- Nothing is printed from the preceding statement. To force the else clause to match the first if clause, you must add a pair of braces: .
- This statement prints B.
public static void main(String[] args) {
public class Main {
public static void main(String[] args) {
int i = 1;
int j = 2;
int k = 3;
if (i > j)
if (i > k)
System.out.println("A");
else
System.out.println("B");
}
}
}
//Solution
public class Main {
public static void main(String[] args) {
int i = 1;
int j = 2;
int k = 3;
if (i > j) {
if (i > k)
System.out.println("A");
}
else
System.out.println("B");
}
}
Tip
Caution
Logical Operators
| # | Operator | Name |
|---|---|---|
| 1 | ! | not |
| 2 | && | and |
| 3 | || | or |
| 4 | ^ | exclusive or |
Truth Table for Operator ! not
Truth Table for Operator && and
Truth Table for Operator || or
Truth Table for Operator ^ exclusive or
Truth Table Examples
switch Statements
- Unlike if-then and if-then-else statements, the switch statement can have a number of possible execution paths.
- A switch works with the byte, short, char, and int primitive data types
- switch logic
switch (status) {
case 0: compute taxes for single filers;
break;
case 1: compute taxes for married file jointly;
break;
case 2: compute taxes for married file separately;
break;
case 3: compute taxes for head of household;
break;
default: System.out.println("Errors: invalid status");
System.exit(1);
}
Switch Examples
switch Statement Flow Chart
Switch Using Lambda Expressions
public class Main {
public static void main(String[] args) {
String dayOfWeek = "Tuesday";
// Using lambda expressions with switch
switch (dayOfWeek) {
case "Monday", "Tuesday", "Wednesday", "Thursday", "Friday"
-> System.out.println("Work day");
case "Saturday", "Sunday" -> System.out.println("Weekend");
default -> System.out.println("Invalid day");
}
}
}
Conditional Operator
- Ternary operator the only operator that accepts three operands: booleanExpression ? expression1 : expression2
- Unary operator
- The unary operators require only one operand; e.g . + , - , ++, -- ,!
- Conditional examples
Conditional Operator or ternary operator Logic
(boolean-expression) ? exp1 : exp2
Frequently-Used Specifiers
| Specifier | Output | Example |
|---|---|---|
| %b | a boolean | true or false |
| %c | a character | 'a' |
| %d | a decimal integer | 200 |
| %f | a floating-point number | 45.4600 |
| %e | a number in standard scientific notation | 4.555e+01 |
| %s | a string | "IS 147" |
Examples Specifier
Unary Single Operand and Binary Two Operands
public class UnaryOperators {
public static void main(String[] args) {
int a = 10;
// Unary plus and minus
System.out.println(+a); // 10
System.out.println(-a); // -10
// Increment and Decrement Operators
System.out.println(++a); // Pre-increment: 11
System.out.println(a++); // Post-increment: 11 (prints before incrementing)
System.out.println(a); // 12 (after post-increment)
System.out.println(--a); // Pre-decrement: 11
System.out.println(a--); // Post-decrement: 11 (prints before decrementing)
System.out.println(a); // 10 (after post-decrement)
// Logical NOT
boolean flag = true;
System.out.println(!flag); // false
}
}
public class BinaryOperators {
public static void main(String[] args) {
int x = 10, y = 5;
// Arithmetic Operators
System.out.println("Addition: " + (x + y)); // 15
System.out.println("Subtraction: " + (x - y));// 5
System.out.println("Multiplication: " + (x * y)); // 50
System.out.println("Division: " + (x / y)); // 2
System.out.println("Modulus: " + (x % y)); // 0
// Relational Operators
System.out.println(x > y); // true
System.out.println(x < y); // false
System.out.println(x == y); // false
System.out.println(x != y); // true
// Logical Operators
System.out.println((x > y) && (x > 0)); // true
System.out.println((x < y) || (x > 0)); // true
// Bitwise Operators
System.out.println(x & y); // 0 (Bitwise AND)
System.out.println(x | y); // 15 (Bitwise OR)
System.out.println(x ^ y); // 15 (Bitwise XOR)
// Assignment Operators
x += y; // x = x + y;
System.out.println(x); // 15
}
}
Examples
- Applying the operator precedence and associativity rule, the expression 3 + 4 * 4 > 5 * (4 + 3) - 1
The Random Class
- The Random class is part of the java.util package
- It provides methods that generate pseudorandom numbers
- A Random object performs complicated calculations based on a seed value to produce a stream of seemingly random values
import java.util.Random
//Using Math class
//If you want to generate a number from 0 to 100 then your code would look like this:
int number1 = (int)(Math.random() * 101);
System.out.println (number1);
//Using Random class
Random rand = new Random ();
int dice = rand.nextInt(6)+1; (0-5) + 1 = 1-6
int dice = rand.nextFloat()*6 +1; (0.0-0.999)*6+1
int bottles = rand.nextInt(100); (0-99)
Random Examples
The Math Class
- The Math class is part of the java.lang package
- The Math class contains methods that perform various mathematical functions
- The methods of the Math class are static methods (also called class methods)
- Static methods can be invoked through the class name – no object of the Math class is needed
value = Math.cos(90) + Math.sqrt(delta);
double circumference = diameter*Math.PI;
int dice= (int) ( Math.random()*6+1);
Math Class Examples
Debugging
Logic errors are called bugs. The process of finding and correcting errors is called debugging. A common approach to debugging is to use a combination of methods to narrow down to the part of the program where the bug is located. You can hand-trace the program (i.e., catch errors by reading the program), or you can insert print statements in order to show the values of the variables or the execution flow of the program. This approach might work for a short, simple program. But for a large, complex program, the most effective approach for debugging is to use a debugger utility.
Debugger
Debugger is a program that facilitates debugging. You can use a debugger to
- Execute a single statement at a time.
- Trace into or stepping over a method.
- Set breakpoints.
- Display variables.
- Display call stack.
- Modify variables.