None match java stream

Java 8 Streams – anyMatch, allMatch, and noneMatch

The anyMatch, allMatch and noneMatch methods are short-circuiting terminal operations on a Java Stream.In this post we will learn about the Java 8 Stream’s anyMatch, allMatch and noneMatch methods.

AnyMatch, AllMatch, and NoneMatch

Let us look at the three methods – anyMatch, allMatch and noneMatch and their signatures.

AnyMatch

boolean anyMatch(Predicate predicate)

We use this terminal method to find if any elements of the stream (at least one) match the provided predicate. It is a short-circuiting because it does not have to evaluate the predicate on all the elements. Example: If the third element satisfies the predicate, then the rest of the stream elements will not be processed. On the other hand, if none of the elements satisfy the predicate, then the entire stream will have to be processed.

AllMatch

boolean allMatch(Predicate predicate)

The allMatch method returns whether all the elements of the stream match the passed predicate. It need not evaluate the predicate on all the elements (say, the first element itself fails to satisfy the predicate). But it has to apply the predicate to all the elements when it returns true.

NoneMatch

boolean noneMatch(Predicate predicate)

Finally, the noneMatch method returns whether no elements of the stream match the predicate. It will not evaluate the predicate on all the elements as it will return false if it finds an element that satisfies the predicate. It will process the entire stream when it returns true (when none of the elements match the predicate).

Examples

For the examples, I will use the below shown Student and Course POJOs.

public class Student < private long id; private String name; private int age; private Listcourses; public Student(long id, String name, int age, List courses) < this.id = id; this.name = name; this.age = age; this.courses = Collections.unmodifiableList(courses); >public long getId() < return id; >public String getName() < return name; >public int getAge() < return age; >public List getCourses() < return courses; >>

Notice the defensive copying of the passed list of courses using Collections.unmodifiableList. This will make the Student class immutable (See the Benefits an immutable class has).

public class Course < private int courseId; private String name; public Course(int courseId, String name) < this.courseId = courseId; this.name = name; >public int getCourseId() < return courseId; >public String getName() < return name; >@Override public int hashCode() < return Objects.hash(courseId); >@Override public boolean equals(Object obj) < if (this == obj) < return true; >if (obj == null) < return false; >if (getClass() != obj.getClass()) < return false; >Course other = (Course) obj; return Objects.equals(courseId, other.courseId); //We consider two courses to be equal if they have the same course id > >

Let us create a list of students where each student has a name, an id, age and studies a list of courses.

Course computerScience = new Course(1, "Computer Science"); Course physics = new Course(2, "Physics"); Course chemistry = new Course(3, "Chemistry"); Course mathematics = new Course(4, "Mathematics"); Course discreteMathematics = new Course(5, "Discrete Mathematics"); Course computerArchitecture = new Course(6, "Computer Architecture"); List students = List.of( new Student(1, "Kelly", 19, List.of(physics, chemistry, mathematics)), new Student(2, "Jon", 20, List.of(computerScience, computerArchitecture, mathematics)), new Student(3, "Joseph", 19, List.of(computerScience, mathematics, discreteMathematics)), new Student(4, "Adam", 20, List.of(computerScience, mathematics)) );

Examples of anyMatch

Let us find if the physics course has been taken by any student at all.

Predicate studentHasPhysicsCourse = student -> student.getCourses().contains(physics); System.out.println(students.stream() .anyMatch(studentHasPhysicsCourse)); //true

We first create a stream of students and pass the predicate studentHasPhysicsCourse to the anyMatch method. It returns true when it evaluates the predicate for the first student. The rest of the stream elements will be skipped.

Let us look at a negative case where none of the elements match the predicate.

Predicate studentAgeMoreThan20 = student -> student.getAge() > 20; System.out.println(students.stream() .anyMatch(studentAgeMoreThan20)); //false

In this case, it would have processed all the elements in the stream before returning false.

Let us look at another example (slightly complicated). Let us check if there is any student who has taken a course that starts with ‘Computer’. The predicate is shown below:

Predicate hasCourseNameStartingWithComputer = student -> student.getCourses().stream() .anyMatch(course -> course.getName().startsWith("Computer"));

The predicate itself has anyMatch operation applied to the stream of courses.

System.out.println(students.stream() .anyMatch(hasCourseNameStartingWithComputer)); //true

Short-circuiting behaviour of anyMatch

Let us add a print statement to the stream pipeline to verify the short-circuiting behaviour of the anyMatch method.

System.out.println(students.stream() .peek(student -> System.out.println("Processing Student: " + student.getName())) .anyMatch(hasCourseNameStartingWithComputer)); //true

Processing Student: Kelly Processing Student: Jon true

When it was processing the second student, the predicate evaluated to true. Hence, it didn’t process the rest of the elements of the stream.

Let us check the same for a negative scenario. Let us check if there is a student whose course name starts with ‘Project’

Predicate hasCourseNameStartingWithProject = student -> student.getCourses().stream() .anyMatch(course -> course.getName().startsWith("Project")); System.out.println(students.stream() .peek(student -> System.out.println("Processing Student: " + student.getName())) .anyMatch(hasCourseNameStartingWithProject)); //false

Processing Student: Kelly Processing Student: Jon Processing Student: Joseph Processing Student: Adam false

Since none of the students will satisfy that predicate, it had to process all the students before returning false.

Examples of allMatch

Predicate used: If a student is less than 21 years.
We pass this predicate to the allMatch method. Since all the students are under 21 years of age, it evaluated to true.

Predicate studentAgeLessThan21 = student -> student.getAge() < 21; System.out.println(students.stream() .allMatch(studentAgeLessThan21)); //true

Another example: Check if all the students have the mathematics course.

Predicate studentHasMathCourse = student -> student.getCourses().contains(mathematics); System.out.println(students.stream() .allMatch(studentHasMathCourse)); //true

Similarly, let us check if all the students have CS course.

Predicate studentHasCSCourse = student -> student.getCourses().contains(computerScience); System.out.println(students.stream() .allMatch(studentHasCSCourse)); //false

Check if all the students have at least one course that starts with ‘Computer’.

Predicate hasCourseNameStartingWithComputer = student -> student.getCourses().stream() .anyMatch(course -> course.getName().startsWith("Computer")); System.out.println(students.stream() .allMatch(hasCourseNameStartingWithComputer)); //false

As before, the predicate construction uses a stream with anyMatch.

Short-circuiting behaviour of allMatch

Let us see how allMatch does short-circuiting of the stream processing by adding a peek statement.

System.out.println(students.stream() .peek(student -> System.out.println("Processing Student: " + student.getName())) .allMatch(hasCourseNameStartingWithComputer)); //true

Processing Student: Kelly false

The first student Kelly does not have a Computer Science course. Hence the predicate failed, and it returned false. The rest of the elements weren’t processed.

When all the elements satisfy the predicate, it would evaluate the predicate against all the elements. Let us go back to the first example (check if students are less than 21).

System.out.println(students.stream() .peek(student -> System.out.println("Processing Student: " + student.getName())) .allMatch(studentAgeLessThan21)); //true

Processing Student: Kelly Processing Student: Jon Processing Student: Joseph Processing Student: Adam true

Examples of noneMatch

Checking if none of the students are less than 21 years of age.

Predicate studentAgeLessThan21 = student -> student.getAge() < 21; System.out.println(students.stream() .noneMatch(studentAgeLessThan21)); //false

Checking if none of the students are more than 21 years of age.

Predicate studentAgeMoreThan21 = student -> student.getAge() > 21; System.out.println(students.stream() .noneMatch(studentAgeMoreThan21)); //true

Short-circuiting behaviour of noneMatch

Let us check if none of the students took computer science.

Predicate studentHasTakenComputerScience = student -> student.getCourses().contains(computerScience); System.out.println(students.stream() .peek(student -> System.out.println("Processing Student: " + student.getName())) .noneMatch(studentHasTakenComputerScience)); //false

Processing Student: Kelly Processing Student: Jon false

The first student didn’t take the CS course, and the predicate was false and hence it continued to the next element in the stream. The second student has the CS course, and the predicate evaluated to true. This caused the noneMatch to return false, and the rest of the elements weren’t processed.

On the other hand, if all the elements failed to satisfy the predicate, it will process all the elements before returning true (Note: We are using noneMatch and hence it returns true only if all the elements failed to match the predicate).

Predicate studentAgeMoreThan20 = student -> student.getAge() > 20; System.out.println(students.stream() .peek(student -> System.out.println("Processing Student: " + student.getName())) .noneMatch(studentAgeMoreThan20)); //true

Processing Student: Kelly Processing Student: Jon Processing Student: Joseph Processing Student: Adam true

Conclusion

In this post we learnt about the Java 8 stream’s anyMatch, allMatch and the noneMatch methods. We looked at the method signatures and what each method does with examples. We also saw the short-circuiting behaviour for each of the methods.

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Java Stream noneMatch()

Here predicate a non-interfering and stateless predicate to apply to elements of the stream.

It is short-circuiting operation. A terminal operation is short-circuiting if, when presented with infinite input, it may terminate in finite time.

• The noneMatch() is a short-circuiting terminal operation.
• It returns whether no element of the stream match the provided predicate.
• It may not evaluate the predicate on all elements if not necessary for determining the result. The method returns true if no stream element matches the given predicate, else method returns false .
• If the stream is empty then true is returned and the predicate is not evaluated.
• It is pretty much opposite to method allMatch().

2. Stream noneMatch() Example

Java example of Stream.noneMatch() method to check if no element in the Stream contains any numeric/digit character.

import java.util.stream.Stream; public class Main < public static void main(String[] args) < Streamstream = Stream.of("one", "two", "three", "four"); boolean match = stream.noneMatch( s -> s.contains("\\d+") ); System.out.println(match); //true > >

Stream.noneMatch() method can be useful in certain cases where we need to run a check on all stream elements. For example, we can use noneMatch() function on a stream of Employee objects to validate that all employees are NOT below a certain age.

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Java 8 Stream – noneMatch() example

In the last tutorial we discussed java stream anyMatch() method. The stream noneMatch() method works just opposite to the anyMatch() method, it returns true if none of the stream elements match the given predicate, it returns false if any of the stream elements matches the condition specified by the predicate.

Java Stream noneMatch() example

import java.util.List; import java.util.function.Predicate; import java.util.ArrayList; class Student < int stuId; int stuAge; String stuName; Student(int id, int age, String name)< this.stuId = id; this.stuAge = age; this.stuName = name; >public int getStuId() < return stuId; >public int getStuAge() < return stuAge; >public String getStuName() < return stuName; >public static List getStudents() < Listlist = new ArrayList<>(); list.add(new Student(11, 28, "Lucy")); list.add(new Student(28, 27, "Kiku")); list.add(new Student(32, 30, "Dani")); list.add(new Student(49, 27, "Steve")); return list; > > public class Example < public static void main(String[] args) < Predicatep1 = s -> s.stuName.startsWith("L"); Predicate p2 = s -> s.stuAge < 28 && s.stuName.startsWith("P"); Listlist = Student.getStudents(); /* noneMatch() method returns true if none of the stream elements matches * the given predicate */ /* This will return false because there is a element in the stream that * matches the condition specified in the predicate p1. * Condition: Student Name should start with letter "L" * Stream element matched: Lucy */ boolean b1 = list.stream().noneMatch(p1); System.out.println("list.stream().noneMatch(p1): "+b1); /* This will return true because none of the elements * matches the condition specified in the predicate p2. * Condition: Student Name should start with letter "P" and age must be >

list.stream().noneMatch(p1): false list.stream().noneMatch(p2): true

The first call to the noneMatch() method with predicate p1 as argument returns false because there is an element in the stream that matches the condition specified by p1.
The second call to the noneMatch() method with predicate p2 as argument returns true because there is no element in the stream that matches the given conditions.

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