Operators and Expressions

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Lesson Goals

  • Learn about the different operators and their functions.
  • Become familiar with Java syntax.

Write practice statements for the arithmetic operators

If variable a holds 10 and variable b holds 15, then:

Operator Operation Description Expression Result
+ addition adds two operands a + b 25
- subtraction subtracts second operand from the first a - b -5
* multiplication multiplies the operands a * b 150
/ division divides first operand by second operand b / a 1
% modulus (remainder) returns the remainder after integer division b % a 5

Write practice statements for the increment
and decrement operators

If variable a holds the value 42, then:

Operator Operation Description Expression Equivalent to… a's value afterwards
++ increment adds one to the value its int operand holds a++ a = a + 1 43
‐‐ decrement subtracts one from the value its int operand holds a-- a = a - 1 41

Write practice statements for the equality operators

If variable a holds 10 and variable b holds 15, then:

Operator Operation Description Expression Result
== equal to evaluates to true if the two operands are equal a == 10
a == b		 true
false
!= not equal to evaluates to true if the two operands are not equal a != 10
a != b		 false
true

Write practice statements for the relational operators

If variable a holds 10 and variable b holds 15, then:

Operator Operation Description Expression Result
> greater than evaluates to true of the first operand is greater than the second operand a > b false
>= greater than or equal to evaluates to true of the first operand is greater than or equal to the second operand a >= b
a >= 10		 false
true
< less than evaluates to true of the first operand is less than the second operand a < b true
<= less than or equal to evaluates to true of the first operand is less than or equal to the second operand a <= b
a <= 10		 true
true

Write practice statements for the logical operators

If variable a holds true and variable b holds false, then:

Operator Operation Description Expression Result
&& conditional AND evaluates to true if both operands are true;
otherwise, evaluates to false		 a && b
a && true		 false
true
|| conditional OR evaluates to true if either operand is true;
otherwise, evaluates to false		 a || b
b || false		 true
false

Translating English to Java

Let's translate English statements into Java. First, we'll do one together.

Start by writing the statements as comments. Here's an example:

// Jessica is 23 years old.
int jessicaAge = 23;

// Sam is 47.
int samAge = 47;

// Jessica is younger than Sam.
System.out.println(jessicaAge < samAge);

Let's break it down…

Defining a variable to hold Jessica's age:

We need to create a variable to hold the age of Jessica. What should its type be?

// Jessica is 23 years old.

Since we think of ages as whole numbers, we will use an int:

int jessicaAge

Let's break it down…

Assigning a value for Jessica's age:

The word "is" means equals. How do we represent assignment?

// Jessica is 23 years old.

If Jessica "is 23", then Jessica's age = 23:

int jessicaAge = 23;

Let's break it down…

Comparing Jessica's and Sam's ages:

To say Jessica is younger than Sam means we are comparing their ages. Which operator would we use to compare them?

// Jessica is younger than Sam.

We use the "less than" relational operator to perform this comparison:

System.out.println(jessicaAge < samAge);

Let's look at the syntax

Single line comments start with //:

// Jessica is 23 years old.
int jessicaAge = 23;
// Sam is 47.
int samAge = 47;
// Jessica is younger than Sam.
System.out.println(jessicaAge < samAge);

Let's look at the syntax

Each statement ends with a semicolon. It acts like a period (.) in English at the end of a sentence.

// Jessica is 23 years old.
int jessicaAge = 23;
// Sam is 47.
int samAge = 47;
// Jessica is younger than Sam.
System.out.println(jessicaAge < samAge);

The statement:

int jessicaAge = 23;

reads as "Jessica's age is 23."

Let's look at the syntax

println is a method, so it ends with a set of opening and closing parentheses:

System.out.println(jessicaAge < samAge);

Inside the parentheses, we find the method arguments. For the println method, this is what we want to print. In this case, that's whether Jessica is younger than Sam:

System.out.println(jessicaAge < samAge);

Your turn! Try translating these word problems into Java.

  • Lisa is cooking muffins. The recipe calls for 7 cups of sugar. She has already put in 2 cups. How many more cups does she need to put in?
  • At a restaurant, Mike and his three friends decided to divide the bill evenly. If each person paid $13 then what was the total bill?
  • How many packages of diapers can you buy with $40 if one package costs $8?
  • Last Friday Trevon had $29. Over the weekend he received some money for cleaning the attic. He now has $41. How much money did he receive?
  • Last week Julia ran 30 miles more than Pranav. Julia ran 47 miles. How many miles did Pranav run?
  • How many boxes of envelopes can you buy with $12 if one box costs $3?
  • After paying $5.12 for a salad, Norachai has $27.10. How much money did he have before buying the salad?

Just keep coding! Just keep coding!

  • 331 students went on a field trip. Six buses were filled and 7 students traveled in cars. How many students were in each bus?
  • Aliyah had $24 to spend on seven pencils. After buying them she had $10. How much did each pencil cost?
  • The sum of three consecutive numbers is 72. Print these numbers consecutively to the console.
  • The sum of three consecutive even numbers is 48. What is the smallest of these numbers?
  • Maria has boxes. She buys seven more. A week later, half of her boxes are destroyed in a fire, leaving her with 22 boxes. With how many did she start?