array assignment operators in java

Array Operations in Java

Last updated: January 8, 2024

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1. Overview

Any Java developer knows that producing a clean, efficient solution when working with array operations isn’t always easy to achieve. Still, they’re a central piece in the Java ecosystem – and we’ll have to deal with them on several occasions.

For this reason, it’s good to have a ‘cheat sheet’ – a summary of the most common procedures to help us tackle the puzzle quickly. This tutorial will come in handy in those situations.

2. Arrays and Helper Classes

Before proceeding, it’s useful to understand what is an array in Java, and how to use it. If it’s your first time working with it in Java, we suggest having a look at  this previous post  where we covered all basic concepts.

Please note that the basic operations that an array supports are, in a certain way, limited. It’s not uncommon to see complex algorithms to execute relatively simple tasks when it comes to arrays.

For this reason, for most of our operations, we’ll be using helper classes and methods to assist us: the  Arrays class provided by Java and the Apache’s ArrayUtils  one.

To include the latter in our project, we’ll have to add the  Apache Commons dependency:

We can check out the latest version of this artifact on Maven Central .

3. Get the First and Last Element of an Array

This is one of the most common and simple tasks thanks to the access-by-index nature of arrays.

Let’s start by declaring and initializing an int array that will be used in all our examples (unless we specify otherwise):

Knowing that the first item of an array is associated with the index value 0 and that it has a length attribute that we can use, then it’s simple to figure out how we can get these two elements:

4. Get a Random Value from an Array

By using the java.util.Random object we can easily get any value from our array:

5. Append a New Item to an Array

As we know, arrays hold a fixed size of values. Therefore, we can’t just add an item and exceed this limit.

We’ll need to start by declaring a new, larger array, and copy the elements of the base array to the second one.

Fortunately, the Arrays class provides a handy method to replicate the values of an array to a new different-sized structure:

Optionally, if the ArrayUtils class is accessible in our project, we can make use of its add method  (or its addAll alternative) to accomplish our objective in a one-line statement:

As we can imagine, this method doesn’t modify the original array object; we have to assign its output to a new variable.

6. Insert a Value Between Two Values

Because of its indexed-values character, inserting an item in an array between two others is not a trivial job.

Apache considered this a typical scenario and implemented a method in its ArrayUtils class to simplify the solution:

We have to specify the index in which we want to insert the value, and the output will be a new array containing a larger number of elements.

The last argument is a variable argument (a.k.a. vararg ) thus we can insert any number of items in the array.

7. Compare Two Arrays

Even though arrays are Object s and therefore provide an equals method, they use the default implementation of it, relying only on reference equality.

We can anyhow invoke the java.util.Arrays ‘ equals method to check if two array objects contain the same values:

Note: this method is not effective for jagged arrays . The appropriate method to verify multi-dimensional structures’ equality is the Arrays.deepEquals one.

8. Check if an Array Is Empty

This is an uncomplicated assignment having in mind that we can use the  length attribute of arrays:

Moreover, we also have a null-safe method in the ArrayUtils helper class that we can use:

This function still depends on the length of the data structure, which considers nulls and empty sub-arrays as valid values too, so we’ll have to keep an eye on these edge cases:

9. How to Shuffle the Elements of an Array

In order to shuffle the items in an array, we can use the  ArrayUtil ‘s feature:

This is a void method and operates on the actual values of the array.

10. Box and Unbox Arrays

We often come across methods that support only Object -based arrays.

Again the ArrayUtils helper class comes in handy to get a boxed version of our primitive array:

The inverse operation is also possible:

11. Remove Duplicates from an Array

The easiest way of removing duplicates is by converting the array to a Set implementation.

As we may know, Collection s use Generics and hence don’t support primitive types.

For this reason, if we’re not handling object-based arrays as in our example, we’ll first need to box our values:

Note: we can use  other techniques to convert between an array and a Set object as well.

Also, if we need to preserve the order of our elements, we must use a different Set implementation, such as a  LinkedHashSet .

12. How to Print an Array

Same as with the equals method, the array’s toString function uses the default implementation provided by the Object class, which isn’t very useful.

Both Arrays and ArrayUtils  classes ship with their implementations to convert the data structures to a readable String .

Apart from the slightly different format they use, the most important distinction is how they treat multi-dimensional objects.

The Java Util’s class provides two static methods we can use:

• toString : doesn’t work well with jagged arrays
• deepToString : supports any Object -based arrays but doesn’t compile with primitive array arguments

On the other hand, Apache’s implementation offers a single toString method that works correctly in any case:

13. Map an Array to Another Type

It’s often useful to apply operations on all array items, possibly converting them to another type of object.

With this objective in mind, we’ll try to create a flexible helper method using Generics:

If we don’t use Java 8 in our project, we can discard the  Function argument, and create a method for each mapping that we need to carry out.

We can now reuse our generic method for different operations. Let’s create two test cases to illustrate this:

For primitive types, we’ll have to box our values first.

As an alternative, we can turn to Java 8’s Streams  to carry out the mapping for us.

We’ll need to transform the array into a Stream  of Object s first. We can do so with the Arrays.stream method.

For example, if we want to map our int values to a custom String representation, we’ll implement this:

14. Filter Values in an Array

Filtering out values from a collection is a common task that we might have to perform in more than one occasion.

This is because at the time we create the array that will receive the values, we can’t be sure of its final size. Therefore, we’ll rely on the Stream s approach again.

Imagine we want to remove all odd numbers from an array:

15. Other Common Array Operations

There are, of course, plenty of other array operations that we might need to perform.

Apart from the ones shown in this tutorial, we’ve extensively covered other operations in the dedicated posts:

• Check if a Java Array Contains a Value
• How to Copy an Array in Java
• Removing the First Element of an Array
• Finding the Min and Max in an Array with Java
• Find Sum and Average in a Java Array
• How to Invert an Array in Java
• Join and Split Arrays and Collections in Java
• Combining Different Types of Collections in Java
• Find All Pairs of Numbers in an Array That Add Up to a Given Sum
• Sorting in Java
• Efficient Word Frequency Calculator in Java
• Insertion Sort in Java

16. Conclusion

Arrays are one of the core functionalities of Java, and therefore it’s really important to understand how they work and to know what we can and can’t do with them.

In this tutorial, we learned how we can handle array operations appropriately in common scenarios.

As always, the full source code of the working examples is available over on  our Github repo .

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The Java Tutorials have been written for JDK 8. Examples and practices described in this page don't take advantage of improvements introduced in later releases and might use technology no longer available. See Java Language Changes for a summary of updated language features in Java SE 9 and subsequent releases. See JDK Release Notes for information about new features, enhancements, and removed or deprecated options for all JDK releases.

Assignment, Arithmetic, and Unary Operators

The simple assignment operator.

One of the most common operators that you'll encounter is the simple assignment operator " = ". You saw this operator in the Bicycle class; it assigns the value on its right to the operand on its left:

This operator can also be used on objects to assign object references , as discussed in Creating Objects .

The Arithmetic Operators

The Java programming language provides operators that perform addition, subtraction, multiplication, and division. There's a good chance you'll recognize them by their counterparts in basic mathematics. The only symbol that might look new to you is " % ", which divides one operand by another and returns the remainder as its result.

The following program, ArithmeticDemo , tests the arithmetic operators.

This program prints the following:

You can also combine the arithmetic operators with the simple assignment operator to create compound assignments . For example, x+=1; and x=x+1; both increment the value of x by 1.

The + operator can also be used for concatenating (joining) two strings together, as shown in the following ConcatDemo program:

By the end of this program, the variable thirdString contains "This is a concatenated string.", which gets printed to standard output.

The Unary Operators

The unary operators require only one operand; they perform various operations such as incrementing/decrementing a value by one, negating an expression, or inverting the value of a boolean.

The following program, UnaryDemo , tests the unary operators:

The increment/decrement operators can be applied before (prefix) or after (postfix) the operand. The code result++; and ++result; will both end in result being incremented by one. The only difference is that the prefix version ( ++result ) evaluates to the incremented value, whereas the postfix version ( result++ ) evaluates to the original value. If you are just performing a simple increment/decrement, it doesn't really matter which version you choose. But if you use this operator in part of a larger expression, the one that you choose may make a significant difference.

The following program, PrePostDemo , illustrates the prefix/postfix unary increment operator:

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Java Assignment Operators

Java Assignment Operators are used to optionally perform an action with given operands and assign the result back to given variable (left operand).

The syntax of any Assignment Operator with operands is

In this tutorial, we will learn about different Assignment Operators available in Java programming language and go through each of these Assignment Operations in detail, with the help of examples.

Operator Symbol – Example – Description

The following table specifies symbol, example, and description for each of the Assignment Operator in Java.

Simple Assignment

In the following example, we assign a value of 2 to x using Simple Assignment Operator.

Addition Assignment

In the following example, we add 3 to x and assign the result to x using Addition Assignment Operator.

Subtraction Assignment

In the following example, we subtract 3 from x and assign the result to x using Subtraction Assignment Operator.

Multiplication Assignment

In the following example, we multiply 3 to x and assign the result to x using Multiplication Assignment Operator.

Division Assignment

In the following example, we divide x by 3 and assign the quotient to x using Division Assignment Operator.

Remainder Assignment

In the following example, we divide x by 3 and assign the remainder to x using Remainder Assignment Operator.

Bitwise AND Assignment

In the following example, we do bitwise AND operation between x and 3 and assign the result to x using Bitwise AND Assignment Operator.

Bitwise OR Assignment

In the following example, we do bitwise OR operation between x and 3 and assign the result to x using Bitwise OR Assignment Operator.

Bitwise XOR Assignment

In the following example, we do bitwise XOR operation between x and 3 and assign the result to x using Bitwise XOR Assignment Operator.

Left-shift Assignment

In the following example, we left-shift x by 3 places and assign the result to x using Left-shift Assignment Operator.

Right-shift Assignment

In the following example, we right-shift x by 3 places and assign the result to x using Right-shift Assignment Operator.

In this Java Tutorial , we learned what Assignment Operators are, and how to use them in Java programs, with the help of examples.

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Arrays are used to store multiple values in a single variable, instead of declaring separate variables for each value.

To declare an array, define the variable type with square brackets :

We have now declared a variable that holds an array of strings. To insert values to it, you can place the values in a comma-separated list, inside curly braces:

To create an array of integers, you could write:

Access the Elements of an Array

You can access an array element by referring to the index number.

This statement accesses the value of the first element in cars:

Try it Yourself »

Note: Array indexes start with 0: [0] is the first element. [1] is the second element, etc.

Change an Array Element

To change the value of a specific element, refer to the index number:

Array Length

To find out how many elements an array has, use the length property:

Test Yourself With Exercises

Create an array of type String called cars .

Start the Exercise

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Interesting facts about Array assignment in Java

Prerequisite : Arrays in Java

While working with arrays we have to do 3 tasks namely declaration, creation, initialization or Assignment. Declaration of array :

Creation of array :

Initialization of array :

Some important facts while assigning elements to the array:

Reference : https://docs.oracle.com/javase/specs/jls/se7/html/jls-10.html

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Array assignment and reference in Java

I have initialized array a and assigning reference of a to new array b. Now I initialized a new array c and passed its reference to array a. Since array b is reference to array a, b should have new values that are in c but b is having old values of a. What is the reason behind it? Output is given below -

• Thats fine this is how each programming language works. –  bit-shashank Commented Jun 24, 2017 at 4:27

5 Answers 5

Don't be irritated by the name 'list'. The images are taken from a python visualization, but the principle is the same in Java

Array a is assigned with a new array:

Array b is assigned to the instance behind a :

Array c is assigned with a new array:

And finally a is assigned to the instance behind c , b was not re-assigned and still keeps a reference to the old a :

Images taken from a visualization on pythontutor.com

Suppose you think of an object as a house, and a reference as a piece of paper with the address of a house written on it. a , b , and c are all references. So when you say

you're building a house with 1, 2, 3, 4, and 5 in it; and a is a piece of paper with the address of that house.

b is another reference, which means it's another piece of paper. But it has the address of the same house on it.

Now we build a new house and put 6, 7, and 8 into it. c will be a piece of paper with the address of the new house. When we say a = c , then the slip of paper that used to be a is thrown out, and we make a new piece of paper with the address of the new house. That's the new value of a .

But b was a separate piece of paper. It hasn't changed. Nothing we've done has changed it.

References are like that.

When you assigned value of a to b, it means b is referring to same space allocated to array a. This means b will pick up any changes made to the array a, but if any changes made to the variable a. If a is made to refer to new array, b will still refer the old a reference.

When you do b=a b references to a. However when you to a=c a is referring to c, but still b refers to the old object (address of this object as value been assigned and it is constant) a that you assigned because that is what it contains when you assigned.

Unless you reassign it, it won't change.

This is why:

What is Object Reference Variable?

You have 2 objects (the arrays) and 3 references (a, b, c) to the objects. You're just swapping around where things are pointed.

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