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Copying arrays

Learn to copy with System.arraycopy.

Copying arrays

System.arraycopy copies a portion of one array into another. It takes five parameters:

int[] src = {1, 2, 3};
int[] dest = new int[3];
System.arraycopy(src, 0, dest, 0, 3);
// dest = {1, 2, 3}

The parameters are: source array, source start index, destination array, destination start index, number of elements to copy. The destination must be large enough; otherwise an exception is thrown.

arraycopy parameters

System.arraycopy(src, srcPos, dest, destPos, length) — five parameters in order:

  • src: source array
  • srcPos: source start index
  • dest: destination array
  • destPos: destination start index
  • length: number of elements to copy

For example, System.arraycopy(src, 1, dest, 0, 2) copies 2 elements starting from src's index 1 into dest's index 0. For partial copies, adjust srcPos and length.

Practice Copy an array and print

Write a Main class with a main method. Assign {1, 2, 3} to int[] src. Assign new int[3] to int[] dest. Copy with System.arraycopy(src, 0, dest, 0, 3). Print the destination's first element with System.out.println(dest[0]).

Sample solution

Main.java
public class Main {
    public static void main(String[] args) {
        int[] src = {1, 2, 3};
        int[] dest = new int[3];
        System.arraycopy(src, 0, dest, 0, 3);
        System.out.println(dest[0]);
    }
}

Expected output

1

Questions and answers

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

1 Complete the arraycopy call

Question 
System.array____(src, 0, dest, 0, 3);
Answer 
System.arraycopy(src, 0, dest, 0, 3);

Explanation: System.arraycopy copies with five parameters.

2 Match the arraycopy parameters

Term Meaning
src Source
dest Destination
srcPos Source start
length Element count

3 System.arraycopy(src, 0, dest, 0, n) — what is n?

  • The source array
  • Number of elements to copy Correct answer
  • The destination array
  • The start index

Explanation: n is the number of elements to copy.

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