24sp ver.

Note: this is for the Spring 2024 iteration of CSE 121. Looking for a different quarter? Please visit https://courses.cs.washington.edu/courses/cse121/.

Relational and Logical Operators

(evaluate expressions as true or false)

Example

if (num < 0) {
    System.out.println("Negative!!");
} else if (num <= 5) {
    System.out.println("I'm small.");
} else {
    System.out.println("I'm big.");
}

Relational Operators

Operator Description
< less than
<= less than or equal
> greater than
>= greater than or equal
== equal
!= not equal

Logical Operators

Operator Description
&& and
|| or
! not

Conditionals and Conditional Statement Structures

(changing execution of program depending on values)

If Conditional Statement

Use case: Want to execute a certain block of statement(s) in one particular case.

Pattern

if (condition) {
    // code block - executed if condition is true
}

Example

int num = 5;
if (num < 10) {
    System.out.println("num is smaller than 10!");
}

Output

num is smaller than 10!

If/Else Conditional Statement

Use case: Use when dealing with one or two cases (“this OR that!”).

Pattern

if (condition) {
    // code block - executed if condition is true
} else {
    // code block - executed if condition is false
}

Example

int num = 12;
if (num < 10) {
    System.out.println("num is smaller than 10!");
} else {
    System.out.println("num is larger or equal to 10!");
}

Output

num is larger or equal to 10!

If/Else-if Conditional Statement

Use case: Want to evaluate specific cases, not just one or the other.

Pattern

if (condition1) {
    // code block - executed if condition1 is true
} else if (condition2) {
    // code block - executed if condition2 is true (and if condition1 is false)
}

Example

int num = 10;
if (num < 10) {
    System.out.println("num is smaller than 10!");
} else if (num == 10) {
    System.out.println("num is equal to 10!");
}

Output

num is equal to 10!

If/Else-if/Else Conditional Statement

Use case: Use when you want to evaluate specific cases along with including a default case (“this OR this OR that!”).

Pattern

if (condition1) {
    // code block - executed if condition1 is true
} else if (condition2) {
    // code block - executed if condition2 is true (and if condition1 is false)
} else {
    // code block - executed if all conditions are false
}

Example

int num = 12;
if (num < 10) {
    System.out.println("num is smaller than 10!");
} else if (num == 10) {
    System.out.println("num is equal to 10!");
} else {
    System.out.println("num is larger than 10!");
}

Output

num is larger than 10!

If and If Conditional Statements

Use case: Want to evaluate multiple blocks of statements based on specific test cases.

Pattern

if (condition1) {
    // code block - executed if condition1 is true
}

if (condition2) {
    // code block - executed if condition2 is true
}

Example

int num = 5;
if (num < 10) {
    System.out.println("num is smaller than 10!");
}
if (num < 2) {
    System.out.println("num is smaller than 2!");
}

Output

num is smaller than 10!