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If/Else Statements

If/Else Statements#

Info

In the following section, we will not include the class definition or main method to focus on the syntax at hand.

Comparisons#

Very commonly, we use booleans when comparing two numbers. Java provides operators to compare two numbers with the following syntax.

int x = 4;
int y = 5;
System.out.println(x == y);  // Equal
System.out.println(x != y);  // Not equal
System.out.println(x < y);   // Less than
System.out.println(x <= y);  // Less than or equal to
System.out.println(x > y);   // Greater than
System.out.println(x >= y);  // Greater than or equal to

x = 4
y = 5
print(x == y)
print(x != y)
print(x < y)
print(x <= y)
print(x > y)
print(x >= y)

let x = 4;
let y = 5;
console.log(x === y);
console.log(x !== y);
console.log(x < y);
console.log(x <= y);
console.log(x > y);
console.log(x >= y);

int x = 4;
int y = 5;
printf("%d\n", x == y);  // Equal
printf("%d\n", x != y);  // Not equal
printf("%d\n", x < y);   // Less than
printf("%d\n", x <= y);  // Less than or equal to
printf("%d\n", x > y);   // Greater than
printf("%d\n", x >= y);  // Greater than or equal to

int x = 4;
int y = 5;
cout << (x == y) << endl;  // Equal
cout << (x != y) << endl;  // Not equal
cout << (x < y) << endl;   // Less than
cout << (x <= y) << endl;  // Less than or equal to
cout << (x > y) << endl;   // Greater than
cout << (x >= y) << endl;  // Greater than or equal to

Boolean Operators#

Booleans represent true or false values. You can combine boolean values using the logical operators:

  • a && b for “and”. This evaluates to true if and only if both a and b are true, otherwise it is false.

  • a || b for “or”. This evaluates to true if any of a or b are true. It is only false if both a and b are false.

  • !a for “not”. This “negates” the value such that is false if a was true, otherwise it is true if a was false.

The following code shows how to use these operators.

boolean b1 = true;
boolean b2 = false;
boolean b3 = b1 && b2;
boolean b4 = b3 || !b2;
boolean b5 = b3 == b4;

b1 = True
b2 = False
b3 = b1 and b2
b4 = b3 or not b2
b5 = b3 == b4

let b1 = true;
let b2 = false;
let b3 = b1 && b2;
let b4 = b3 || !b2;
let b5 = b3 === b4;

int b1 = 1;
int b2 = 0;
int b3 = b1 && b2;
int b4 = b3 || !b2;
int b5 = b3 == b4;

bool b1 = true;
bool b2 = false;
bool b3 = b1 && b2;
bool b4 = b3 || !b2;
bool b5 = b3 == b4;

Test your understanding: What is the value of b4?

b4 is true. To figure this out, we can identify the value of each variable.

  • b1 is true

  • b2 is false

  • b3 is false because b1 && b2 evaluates to false (at least one argument is false`).

  • b4 is true. To evaluate b3 || !b2 we first evaluate !b2 to get true, and then b3 || true is true

  • b5 is false because b3 is false and b4 is true, which means they are not equal.

Conditionals#

Conditional statements or if/else statements in Java behave similarly to other languages. Important things to note about conditionals in Java are:

  • if and else if statements require parentheses around their conditions.

  • Java uses curly brackets ({}) to denote the opening and closing of an if/ese statement’s body. Anything inside the curly brackets of a if/else statement only run if the condition for that block is met.

  • Proper indentation is not a requirement of the Java language, but it is strongly recommended that you use proper indentation to show what lines of code belong inside/outside the body of an if statement.

int n = 4;
if (n % 3 == 0) {
    System.out.println("Case 0");
} else if (n % 3 == 1 || n % 2 == 0) {
    System.out.println("Case 1");
} else {
    System.out.println("Case 2");
}
System.out.println("After if/else");

n = 4
if n % 3 == 0:
    print('Case 0')
elif n % 3 == 1 or n % 2 == 0:
    print('Case 1')
else:
    print('Case 2')
print('After if/else')

let n = 4;
if (n % 3 === 0) {
    console.log('Case 0');
} else if (n % 3 === 1 || n % 2 === 0) {
    console.log('Case 1');
} else {
    console.log('Case 2');
}
console.log('After if/else');

int n = 4;
if (n % 3 == 0) {
    printf("Case 0\n");
} else if (n % 3 == 1 || n % 2 == 0) {
    printf("Case 1\n");
} else {
    printf("Case 2\n");
}
printf("After if/else\n");

int n = 4;
if (n % 3 == 0) {
    cout << "Case 0" << endl;
} else if (n % 3 == 1 || n % 2 == 0) {
    cout << "Case 1" << endl;
} else {
    cout << "Case 2" << endl;
}
cout << "After if/else" << endl;

The output of this block is

Case 1
After if/else
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