How to set Operations in Java

How to set Operations in Java

Now we will see some of the basic operations on the Set i.e. Union, Intersection and Difference. ... Java code for demonstrating union, intersection and difference.

1. Introduction

A set is a handy way to represent a unique collection of items.

In this tutorial, we’ll learn more about what that means and how we can use one in Java.

2. A Bit of Set Theory

2.1. What Is a Set?

A set is simply a group of unique things. So, a significant characteristic of any set is that it does not contain duplicates.

We can put anything we like into a set. However, we typically use sets to group together things which have a common trait. For example, we could have a set of vehicles or a set of animals.

Let’s use two sets of integers as a simple example:

setA : {1, 2, 3, 4}
 
setB : {2, 4, 6, 8}

We can show sets as a diagram by simply putting the values into circles:

Diagrams like these are known as Venn diagrams and give us a useful way to show interactions between sets as we’ll see later.

2.2. The Intersection of Sets

The term intersection means the common values of different sets.

We can see that the integers 2 and 4 exist in both sets. So the intersection of setA and setB is 2 and 4 because these are the values which are common to both of our sets.

setA intersection setB = {2, 4}

In order to show the intersection in a diagram, we merge our two sets and highlight the area that is common to both of our sets:

2.3. The Union of Sets

The term union means combining the values of different sets.

So let’s create a new set which is the union of our example sets. We already know that we can’t have duplicate values in a set. However, our sets have some duplicate values (2 and 4). So when we combine the contents of both sets, we need to ensure we remove duplicates. So we end up with 1, 2, 3, 4, 6 and 8.

setA union setB = {1, 2, 3, 4, 6, 8}

Again we can show the union in a diagram. So let’s merge our two sets and highlight the area that represents the union:

2.4. The Relative Complement of Sets

The term relative complement means the values from one set that are not in another. It is also referred to as the set difference.

Now let’s create new sets which are the relative complements of setA and setB.

relative complement of setA in setB = {6, 8}
 
relative complement of setB in setA = {1, 3}

And now, let’s highlight the area in setA that is not part of setB. This gives us the relative complement of setB in setA:

2.5. The Subset and Superset

A subset is simply part of a larger set, and the larger set is called a superset. When we have a subset and superset, the union of the two is equal to the superset, and the intersection is equal to the subset.

3. Implementing Set Operations with java.util.Set

In order to see how we perform set operations in Java, we’ll take the example sets and implement the intersection, union and relative complement. So let’s start by creating our sample sets of integers:

private Set<Integer> setA = setOf(1,2,3,4);
private Set<Integer> setB = setOf(2,4,6,8);
     
private static Set<Integer> setOf(Integer... values) {
    return new HashSet<Integer>(Arrays.asList(values));
}

3.1. Intersection

First, we’re going to use the retainAll method to create the intersection of our sample sets. Because retainAll modifies the set directly, we’ll make a copy of setA called intersectSet. Then we’ll use the retainAll method to keep the values that are also in setB:

Set<Integer> intersectSet = new HashSet<>(setA);
intersectSet.retainAll(setB);
assertEquals(setOf(2,4), intersectSet);

3.2. Union

Now let’s use the addAll method to create the union of our sample sets. The addAll method adds all the members of the supplied set to the other. Again as addAll updates the set directly, we’ll make a copy of setA called unionSet, and then add setB to it:

Set<Integer> unionSet = new HashSet<>(setA);
unionSet.addAll(setB);
assertEquals(setOf(1,2,3,4,6,8), unionSet);

3.3. Relative Complement

Finally, we’ll use the removeAll method to create the relative complement of setB in setA. We know that we want the values that are in setA that don’t exist in setB. So we just need to removeAll elements from setA that are also in setB:

Set<Integer> differenceSet = new HashSet<>(setA);
differenceSet.removeAll(setB);
assertEquals(setOf(1,3), differenceSet);
4. Implementing Set Operations with Streams

4.1. Intersection

Let’s create the intersection of our sets using Streams.

First, we’ll get the values from setA into a stream. Then we’ll filter the stream to keep all values that are also in setB. And lastly, we’ll collect the results into a new Set:

Set<Integer> intersectSet = setA.stream()
    .filter(setB::contains)
    .collect(Collectors.toSet());
assertEquals(setOf(2,4), intersectSet);

4.2. Union

Now let’s use the static method Streams.concat to add the values of our sets into a single stream.

In order to get the union from the concatenation of our sets, we need to remove any duplicates.We’ll do this by simply collecting the results into a Set:

Set<Integer> unionSet = Stream.concat(setA.stream(), setB.stream())
    .collect(Collectors.toSet());
assertEquals(setOf(1,2,3,4,6,8), unionSet);

4.3. Relative Complement

Finally, we’ll create the relative complement of setB in setA.

As we did with the intersection example we’ll first get the values from setA into a stream. This time we’ll filter the stream to remove any values that are also in setB. Then, we’ll collect the results into a new Set:

Set<Integer> differenceSet = setA.stream()
    .filter(val -> !setB.contains(val))
    .collect(Collectors.toSet());
assertEquals(setOf(1,3), differenceSet);
5. Utility Libraries for Set Operations

Now that we’ve seen how to perform basic set operations with pure Java, let’s use a couple of utility libraries to perform the same operations. One nice thing about using these libraries is that the method names clearly tell us what operation is being performed.

5.1. Dependencies

In order to use the Guava Sets and Apache Commons Collections SetUtils we need to add their dependencies:

<dependency>
    <groupId>com.google.guava</groupId>
    <artifactId>guava</artifactId>
    <version>27.1-jre</version>
</dependency>
<dependency>
    <groupId>org.apache.commons</groupId>
    <artifactId>commons-collections4</artifactId>
    <version>4.3</version>
</dependency>

5.2. Guava Sets

Let’s use the Guava Sets class to perform intersection and union on our example sets. In order to do this we can simply use the static methods union and intersection of the Sets class:

Set<Integer> intersectSet = Sets.intersection(setA, setB);
assertEquals(setOf(2,4), intersectSet);
 
Set<Integer> unionSet = Sets.union(setA, setB);
assertEquals(setOf(1,2,3,4,6,8), unionSet);

Take a look at our Guava Sets article to find out more.

5.3. Apache Commons Collections

Now let’s use the intersection and union static methods of the SetUtils class from the Apache Commons Collections:

Set<Integer> intersectSet = SetUtils.intersection(setA, setB);
assertEquals(setOf(2,4), intersectSet);
 
Set<Integer> unionSet = SetUtils.union(setA, setB);
assertEquals(setOf(1,2,3,4,6,8), unionSet);

Take a look at our Apache Commons Collections SetUtils tutorial to find out more.

6. Conclusion

We’ve seen an overview of how to perform some basic operations on sets, as well as details of how to implement these operations in a number of different ways.

Originally published on https://www.baeldung.com

Java Fundamentals: Learn Java for absolute beginners |Simpliv

Java Fundamentals: Learn Java for absolute beginners |Simpliv

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Types of Data in Java and how they are classified

Management and Classification of operators in Java

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Use of the do-while loop and when to use it

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Introduction to Object Oriented Programming (OOP)

Handling Classes in Java

Use of Objects in Java

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Declaration of Methods or Functions in Java

Use and call of functions in Java

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Using Arrays in Java

Management of Matrices in Java

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Use of superclasses and subclasses in Java

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We will study the concept of Inheritance in Java
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Java Essentials : Learn Core Java From Basic to Advance

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Fundamentos de Java: Aprende Java desde cero, sin misterios | Simpliv

Fundamentos de Java: Aprende Java desde cero, sin misterios | Simpliv

Fundamentos de Java: Aprende Java desde cero, sin misterios

Description
This is the best course to learn to program in Java in Spanish from scratch and without any experience in this fabulous programming language . This is the first course where we will study the Java Fundamentals, and we will take you step by step until you acquire the basics of the Java language and so you can start studying more advanced Java topics.

The content is divided into perfectly structured levels , each level supported by the previous one, with the aim of adding Java knowledge incrementally so that you can focus on mastering the issues little by little and gradually. So ensure the success of your Java training.

In other offer support of any doubt teaching materials included in this course Fundamentals of Java.

To make matters worse, we handle a new teaching methodology that we have called Speed ​​Learning. This methodology consists of concise videos that go directly to the point to study, complemented with eBooks with explanations and step-by-step images (which you can print, or search for any text you need, or use for your offline study), since as we know we cannot do text search within a video. In addition, our methodology includes perfectly structured and very didactic exercises, which will allow you to accelerate your eLearning learning. Without wasting time on videos where you have to watch the instructor codify an exercise, too much theory, little practice or anything like that. Our Speed ​​Learning methodology guarantees that in the shortest possible time you will acquire the necessary knowledge for the professional and professional world of Java.

The Java Fundamentals course includes the following topics of study:

Level. Java basics

Lesson 1 - Starting with Java Technology

The amazing world of Java programming
What is Java technology (from a practical approach)
Our first Java program from scratch
Lesson 2 - Variables and Operators in Java

Use of Variables in Java and what we use them for
Data types in Java and how they are classified
Operator Management and Classification in Java
Lesson 3 - Control sentences in Java

Use of the if-else structure and where to use it
Management of the switch structure and when to apply it
Lesson 4 - Cycle Management in Java

Use of the for cycle and its use
Use of the while cycle and how to apply it
Use of the do-while cycle and when to use it
Lesson 5 - Object Oriented Programming

Introduction to Object Oriented Programming (OOP)
Class Management in Java
Using Objects in Java
Lesson 6 - Functions in Java

Declaration of Methods or Functions in Java
Use and call of functions in Java
Lesson 7 - Data Management in Java

Using Arrangements in Java
Matrix Management in Java
Lesson 8 - Inheritance in Java

Inheritance Management in Java
Use of superclasses and subclasses in Java
Final Level Laboratory

Final Exercise where everything learned in this Level is integrated
At the end you get a certificate of having completed the Java Fundamentals course.

We wait for you from the other side.

Ing. Ubaldo Acosta

Founder of Global Mentoring

Passion for Java Technology

Who this course is for:

Anyone who wants to learn to program in Java
Basic knowledge
Basic knowledge of PC use
Basic operation of an operating system such as Windows, Mac or Linux
It is not required to know how to program, we will start from scratch !!!
The attitude and desire to start coding and learning Java once and for all from scratch !!!
What will you learn
Have the basics of the programming language with Java
You will know the basic syntax of the Java language
Will handle the concept of Variables and Operators in Java
We will study Object Oriented Programming with Java
You will learn Control Sentences and Cycles in Java
We will see the concept of Functions with Java
We will study the concept of Inheritance in Java
We will learn to use Arrangements in java
We will handle the concept of Matrices in Java
We will learn to Design Classes in Java
We will make a final application with everything learned in the course
To continue: