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Summary - Method parameters

Combine primitive, object and varargs to write a statistics function.

Summary: Method parameters

In this group you saw four aspects of parameter passing: primitive pass by value, object references, varargs and final parameters.

Primitive parameters are copied; the outside is not affected. Object parameters pass a copy of the reference; content changes affect the outside. With varargs you can accept a flexible number of arguments. final prevents reassignment.

Now you will combine these to write a small statistics function: take numbers via varargs and return min and max as an array.

Practice Statistics function

Define a static int[] method called minMax; parameter int... nums. The body should scan all elements to find the smallest and the largest; return new int[]{min, max}. In main, call minMax(4, 9, 2, 7) and print the result with Arrays.toString.

Starter code

Main.java
import java.util.Arrays;

public class Main {
  public static void main(String[] args) {
    // Call the method with four values, print the result
  }
  // Define the minMax method here (varargs)
}

Sample solution

Main.java
static int[] minMax(int... nums) {
  int min = Integer.MAX_VALUE;
  int max = Integer.MIN_VALUE;
  for (int n : nums) {
    if (n < min) min = n;
    if (n > max) max = n;
  }
  return new int[]{min, max};
}
// inside main:
System.out.println(Arrays.toString(minMax(4, 9, 2, 7)));

Expected output

[2, 9]

Questions and answers

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

1 Fill in the blank: varargs declaration

Question 
static int[] minMax(int____ nums) {
  int min = Integer.MAX_VALUE;
  int max = Integer.MIN_VALUE;
  for (int n : nums) {
    if (n < min) min = n;
    if (n > max) max = n;
  }
  return new int[]{min, max};
}
Answer 
static int[] minMax(int... nums) {
  int min = Integer.MAX_VALUE;
  int max = Integer.MIN_VALUE;
  for (int n : nums) {
    if (n < min) min = n;
    if (n > max) max = n;
  }
  return new int[]{min, max};
}

Explanation: int... accepts a flexible number of arguments.

2 Match scenario to approach

Term Meaning
Flexible count of numbers varargs
Change the outer list object parameter
Prevent reassignment final parameter
Keep the primitive value safe pass by value

3 Which call is valid for a method with int... nums parameter?

  • sum(1, 2, 3)
  • sum{1, 2, 3}
  • sum([1, 2, 3]) Correct answer
  • sum(int 1, 2, 3)

Explanation: A varargs call takes comma-separated arguments.

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