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int and double

Learn numeric variables with int and double.

int and double

Java has two main types for numbers: int and double.

int holds 32-bit integers: between -2 billion and +2 billion. It does not allow decimals.

double holds 64-bit decimal numbers. The dot (.) separates the decimal part: 3.14.

int age = 25;
double height = 1.78;

Which one you pick depends on the value: int for whole numbers, double for decimals.

double decimals

double holds numbers with a fractional part. The dot is the decimal separator. Scientific notation is supported: 1.5e3 = 1500.0.

double pi = 3.14;
double distance = 1.5e3;
System.out.println(pi);

Dividing two doubles gives a decimal result: 7.0 / 2.0 = 3.5. But 7 / 2 (int division) = 3.

Avoid using double for money; rounding errors may occur. BigDecimal is safer for that.

Practice Define int and double and print them

Write a Main class with a main method. Assign 30 to int age and 1.75 to double height. Print both with println.

Sample solution

Main.java
public class Main {
    public static void main(String[] args) {
        int age = 30;
        double height = 1.75;
        System.out.println(age);
        System.out.println(height);
    }
}

Expected output

30
1.75

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 Which is an int value?

  • 42 Correct answer
  • 3.14
  • "number"
  • true

Explanation: 42 is an integer and is written as an int.

2 Assign a value to an int variable

Question 
int age = ____;
Answer 
int age = 25;

Explanation: An int is assigned without quotes.

3 Match the types

Term Meaning
int Integer
double Decimal
42 Int literal
3.14 Double literal

All lessons in Beginner

1 Java basics

  1. What is Java?
  2. The main method
  3. Comments
  4. Class skeleton
  5. javac and java
  6. Summary - Java basics

2 Variables

  1. int and double
  2. boolean
  3. String
  4. Naming variables
  5. final variables
  6. Summary - Variables

3 Data types

  1. Primitive types
  2. Type casting
  3. String concatenation
  4. Math class
  5. BigInteger and BigDecimal
  6. Summary - Data types

4 Project: Calculator

  1. Project design
  2. Add/subtract
  3. Multiply/divide
  4. Error handling
  5. Putting it together

5 Operators

  1. Arithmetic
  2. Comparison
  3. Logical
  4. Bitwise
  5. Assignment and increment
  6. Summary - Operators

6 String basics

  1. length and charAt
  2. equals and equalsIgnoreCase
  3. indexOf and substring
  4. toUpperCase and trim
  5. String.format
  6. Summary - String basics

7 Conditionals

  1. The if statement
  2. else and else if
  3. Nested if
  4. switch
  5. Ternary
  6. Summary - Conditionals

8 Loops

  1. The for loop
  2. The while loop
  3. do-while
  4. break and continue
  5. for-each
  6. Summary - Loops

9 Project: Shopping cart

  1. Cart design
  2. Adding items
  3. Calculating totals
  4. Updating quantity
  5. Putting it together

10 Arrays

  1. Declaring arrays
  2. Array access
  3. Filling arrays
  4. Multi-dimensional arrays
  5. Copying arrays
  6. Summary - Arrays

11 Array methods

  1. Arrays.sort
  2. Arrays.toString
  3. Arrays.binarySearch
  4. Arrays.copyOf
  5. Arrays.fill
  6. Summary - Array methods

12 Collections

  1. ArrayList
  2. add and get
  3. HashMap
  4. put and get
  5. HashSet
  6. Summary - Collections

13 Methods

  1. Defining methods
  2. return
  3. void methods
  4. Method overloading
  5. Scope
  6. Summary - Methods

14 Method parameters

  1. Primitive parameters
  2. Object parameters
  3. varargs
  4. Multiple values via array
  5. final parameters
  6. Summary - Method parameters

15 Project: To-do CLI

  1. Task model
  2. Adding tasks
  3. Listing tasks
  4. Completing tasks
  5. Putting it together

16 String builder

  1. StringBuilder
  2. append
  3. insert and delete
  4. reverse
  5. toString
  6. Summary - String builder

17 Input and output

  1. Scanner
  2. nextInt and nextLine
  3. System.out.printf
  4. BufferedReader
  5. try-with-resources
  6. Summary - Input and output

18 Enum

  1. Declaring enums
  2. values and valueOf
  3. Enum fields
  4. Enum methods
  5. switch with enum
  6. Summary - Enum

19 Exception basics

  1. try/catch
  2. finally
  3. throw
  4. Exception hierarchy
  5. Multiple catch
  6. Summary - Exception basics

20 Beginner final

  1. Project design
  2. Data model
  3. Business logic
  4. Error handling
  5. Putting it together