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Summary - Data types

Combine primitives, Math and BigDecimal to write an interest calculator.

Summary - Data types

In this group you learned Java's data types:

  • Primitive types: byte, short, int, long, float, double, char, boolean
  • Type casting: widening (automatic), narrowing (cast)
  • String concatenation: + operator
  • Math class: abs, max, min, pow, PI
  • BigDecimal: for precise money calculations

Now combine them and write an interest calculator.

Practice Compute with Math

Write a Main class with a main method. Assign 15 to int a and 8 to int b. Print Math.max(a, b) with println.

Sample solution

Main.java
public class Main {
    public static void main(String[] args) {
        int a = 15;
        int b = 8;
        System.out.println(Math.max(a, b));
    }
}

Expected output

15

Tips

A few tips from this group:

  • Always use BigDecimal for money; double causes rounding loss.
  • Remember the L suffix on long: 10000000000L.
  • char uses single quotes, String uses double quotes.
  • The + operator works left to right; precedence matters.
  • Think about data loss before casting.

These basics are needed for conditionals and loops in the next groups.

Practice Compute interest with BigDecimal

Write a Main class with a main method. Add import java.math.BigDecimal; at the top. Assign BigDecimal.valueOf(1000) to BigDecimal principal and BigDecimal.valueOf(0.05) to BigDecimal rate. Print principal.multiply(rate) with println.

Starter code

Main.java
import java.math.BigDecimal;

public class Main {

}

Sample solution

Main.java
import java.math.BigDecimal;

public class Main {
    public static void main(String[] args) {
        BigDecimal principal = BigDecimal.valueOf(1000);
        BigDecimal rate = BigDecimal.valueOf(0.05);
        System.out.println(principal.multiply(rate));
    }
}

Expected output

50.0

Questions and answers

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

1 Match the types

Term Meaning
int Integer
double Decimal
char Character
BigDecimal Precise

2 Cast to convert

Question 
int whole = ____ 9.99;
Answer 
int whole = (int) 9.99;

Explanation: (int) cast does narrowing conversion.

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