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This tutorial explains the difference between size and length in Java. We have also listed some sample codes to help you understand the topic.

Java has a size()method and a lengthproperty. Beginners may think that they are interchangeable and perform the same task because they sound somewhat the same. In Java, size and length are two different things. Here, we will learn about the difference between the two.

Array lengthProperties in Java

Arrays store a fixed number of data of the same type in an ordered manner. All arrays in Java have a length field which is used to store the space allocated for the elements of that array. It is a constant value which is used to find out the maximum capacity of the array.

• Keep in mind that this field does not give us the number of elements present in the array, but rather the maximum number of elements that can be stored (regardless of whether the elements exist or not).

.lengthExample in Java Array

In the following code, we first initialize an 7array of length . Even though we haven't added any elements, the length field of the array is still displayed 7. This 7simply indicates the maximum capacity.

public class Main {
  public static void main(String[] args) {
    int[] intArr = new int[7];
    System.out.print("Length of the Array is: " + intArr.length);
  }
}

Output:

Length of the Array is: 7

Now, let's add 3 elements to the array using their indices and then print the length field. It still displays 7.

public class Main {
  public static void main(String[] args) {
    int[] intArr = new int[7];
    intArr[0] = 20;
    intArr[1] = 25;
    intArr[2] = 30;
    System.out.print("Length of the Array is: " + intArr.length);
  }
}

Output:

Length of the Array is: 7

The length field is constant because the size of the array is fixed. We have to define the maximum number of elements we will store in the array during initialization (the capacity of the array), and we cannot exceed this limit.

size()Example of methods in Java array

Arrays do not have size()a method; it will return a compilation error. See the example below.

public class SimpleTesting {
  public static void main(String[] args) {
    int[] intArr = new int[7];
    System.out.print("Length of the Array is: " + intArr.size());
  }
}

Output:

Exception in thread "main" java.lang.Error: Unresolved compilation problem: 
	Cannot invoke size() on the array type int[]

	at SimpleTesting.main(SimpleTesting.java:7)

length()Find the length using the method in Java

Java strings are just ordered collections of characters, and unlike arrays, they have length()a method instead of lengtha field. This method returns the number of characters present in the string.

Please refer to the following example.

public class Main {
  public static void main(String[] args) {
    String str1 = "This is a string";
    String str2 = "Another String";
    System.out.println("The String is: " + str1);
    System.out.println("The length of the string is: " + str1.length());
    System.out.println("\nThe String is: " + str2);
    System.out.println("The length of the string is: " + str2.length());
  }
}

Output:

The String is: This is a string
The length of the string is: 16

The String is: Another String
The length of the string is: 14

Note that we cannot use the property on strings length, and length()the method does not work on arrays. The following code shows the error we get when we misuse them.

public class SimpleTesting {
  public static void main(String[] args) {
    String str1 = "This is a string";
    System.out.println("The length of the string is: " + str1.length);
  }
}

Output:

Exception in thread "main" java.lang.Error: Unresolved compilation problem: 
	length cannot be resolved or is not a field

	at SimpleTesting.main(SimpleTesting.java:7)

length()Likewise, we cannot use string methods on arrays .

public class SimpleTesting {
  public static void main(String[] args) {
    int[] intArray = {1, 2, 3};
    System.out.println("The length of the string is: " + intArray.length());
  }
}

Output:

Exception in thread "main" java.lang.Error: Unresolved compilation problem: 
	Cannot invoke length() on the array type int[]

	at SimpleTesting.main(SimpleTesting.java:7)

Java Collections size()Methods

size()is java.util.Collectionsa method of the class. CollectionsThe class is used by many different collections (or data structures), such as ArrayList, LinkedList, HashSetand HashMap.

size()The method returns the number of elements currently present in the collection. Unlike the array's lengthproperty, size()the value returned by the method is not constant, but varies based on the number of elements.

All collections in Java Collection Frameworkare dynamically allocated, so the number of elements may vary. size()The method is used to keep track of the number of elements.

In the code below, it is clear that when we create a new without any elements ArrayList, size()the method returns 0.

import java.util.ArrayList;
import java.util.List;
public class Main {
  public static void main(String[] args) {
    List<Integer> list = new ArrayList<Integer>();
    System.out.println("The ArrayList is: " + list);
    System.out.println("The size of the ArrayList is: " + list.size());
  }
}

Output:

The ArrayList is: []
The size of the ArrayList is: 0

But this value changes as we add or remove elements. After adding three elements, the size increases to 3. Next, we remove two elements and the size of the list becomes 1.

import java.util.ArrayList;
import java.util.List;
public class Main {
  public static void main(String[] args) {
    List<Integer> list = new ArrayList<Integer>();
    System.out.println("The ArrayList is: " + list);
    System.out.println("The size of the ArrayList is: " + list.size());
    list.add(20);
    list.add(40);
    list.add(60);
    System.out.println("\nAfter adding three new elements:");
    System.out.println("The ArrayList is: " + list);
    System.out.println("The size of the ArrayList is: " + list.size());
    list.remove(0);
    list.remove(1);
    System.out.println("\nAfter removing two elements:");
    System.out.println("The ArrayList is: " + list);
    System.out.println("The size of the ArrayList is: " + list.size());
  }
}

Output:

The ArrayList is: []
The size of the ArrayList is: 0

After adding three new elements:
The ArrayList is: [20, 40, 60]
The size of the ArrayList is: 3

After removing two elements:
The ArrayList is: [40]
The size of the ArrayList is: 1

Difference between size and length in Java

Although size and length can sometimes be used in the same context, they have completely different meanings in Java.

The field of an array lengthis used to represent the maximum capacity of the array. The maximum capacity refers to the maximum number of elements that can be stored in it. This field does not take into account the number of elements present in the array and remains unchanged.

The method of a string length()is used to indicate the number of characters that occur in a string. The method Collections Frameworkof size()is used to see how many elements are currently present in the collection. Collectionshas a dynamic size, so size()the return value of may vary.