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Conditionals and Control Flow

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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

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!

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. */

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