Lam Nguyen

August 18, 2023

• 2 min read

Java I Conditionals and Control Flow

else Statement, else if Statements, if Statement, Nested Conditional Statements, Switch Statement, AND Operator, NOT Operator, The OR Operator, Conditional Operators - Order of Evaluation

else Statement

The else statement executes a block of code when the condition inside the if statement is false. The else statement is always the last condition.

boolean condition1 = false;

if (condition1){
    System.out.println("condition1 is true");
}
else{
    System.out.println("condition1 is not true");
}
// Prints: condition1 is not true

else if Statements

else-if statements can be chained together to check multiple conditions. Once a condition is true, a code block will be executed and the conditional statement will be exited.

There can be multiple else-if statements in a single conditional statement.

int testScore = 76;
char grade;

if (testScore >= 90) {
  grade = 'A';
} else if (testScore >= 80) {
  grade = 'B';
} else if (testScore >= 70) {
  grade = 'C';
} else if (testScore >= 60) {
  grade = 'D';
} else {
  grade = 'F';
}

System.out.println("Grade: " + grade); // Prints: C

if Statement

An if statement executes a block of code when a specified boolean expression is evaluated as true.

if (true) {
	System.out.println("This code executes");
}
// Prints: This code executes

if (false) {
	System.out.println("This code does not execute");
}
// There is no output for the above statement

Java Short Hand If…Else (Ternary Operator)

There is also a short-hand if else, which is known as the ternary operator because it consists of three operands.

Instead of writing:

int time = 20;
if (time < 18) {
  System.out.println("Good day.");
} else {
  System.out.println("Good evening.");
}

You can simply write:

int time = 20;
String result = (time < 18) ? "Good day." : "Good evening.";
System.out.println(result);

Nested Conditional Statements

A nested conditional statement is a conditional statement nested inside of another conditional statement. The outer conditional statement is evaluated first; if the condition is true, then the nested conditional statement will be evaluated.

boolean studied = true;
boolean wellRested = true;

if (wellRested) {
  System.out.println("Best of luck today!");
  if (studied) {
    System.out.println("You are prepared for your exam!");
  } else {
    System.out.println("Study before your exam!");
  }
}

// Prints: Best of luck today!
// Prints: You are prepared for your exam!

Java Switch Statement

Instead of writing many if..else statements, you can use the switch statement.

This is how it works:

The switch expression is evaluated once.
The value of the expression is compared with the values of each case.
If there is a match, the associated block of code is executed.
The break and default keywords are optional, and will be described later in this chapter

The example below uses the weekday number to calculate the weekday name:

int day = 4;
switch (day) {
  case 1:
    System.out.println("Monday");
    break;
  case 2:
    System.out.println("Tuesday");
    break;
  case 3:
    System.out.println("Wednesday");
    break;
  case 4:
    System.out.println("Thursday");
    break;
  case 5:
    System.out.println("Friday");
    break;
  case 6:
    System.out.println("Saturday");
    break;
  case 7:
    System.out.println("Sunday");
    break;
}
// Outputs "Thursday" (day 4)

The break Keyword

When Java reaches a break keyword, it breaks out of the switch block.

This will stop the execution of more code and case testing inside the block.

When a match is found, and the job is done, it’s time for a break. There is no need for more testing.

The default Keyword

The default keyword specifies some code to run if there is no case match:

int day = 4;
switch (day) {
  case 6:
    System.out.println("Today is Saturday");
    break;
  case 7:
    System.out.println("Today is Sunday");
    break;
  default:
    System.out.println("Looking forward to the Weekend");
}
// Outputs "Looking forward to the Weekend"

AND Operator

The AND logical operator is represented by &&. This operator returns true if the boolean expressions on both sides of the operator are true; otherwise, it returns false.

System.out.println(true && true); // Prints: true
System.out.println(true && false); // Prints: false
System.out.println(false && true); // Prints: false
System.out.println(false && false); // Prints: false

NOT Operator

The NOT logical operator is represented by !. This operator negates the value of a boolean expression.

boolean a = true;
System.out.println(!a); // Prints: false

System.out.println(!false) // Prints: true

The OR Operator

The logical OR operator is represented by ||. This operator will return true if at least one of the boolean expressions being compared has a true value; otherwise, it will return false.

System.out.println(true || true); // Prints: true
System.out.println(true || false); // Prints: true
System.out.println(false || true); // Prints: true
System.out.println(false || false); // Prints: false

Conditional Operators - Order of Evaluation

If an expression contains multiple conditional operators, the order of evaluation is as follows: Expressions in parentheses -> NOT -> AND -> OR.

boolean foo = true && (!false || true); // true
/*
(!false || true) is evaluated first because it is contained within parentheses.

Then !false is evaluated as true because it uses the NOT operator.

Next, (true || true) is evaluation as true.

Finally, true && true is evaluated as true meaning foo is true. */