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You can convert list or array to
stream very easily and perform various operations on top of it.Java 8 Stream provides various methods such as map, filter, reduce etc.Let’s see more about Java 8 Stream filter method.
As name suggests, filter method is used to filter stream on basis of criterion. You can pass lambda expressions to filter method but it should always return a boolean value. We have already seen how to pass Predicate object to filter method to filter a collection.
Lets understand more with help of example:
Lets say you have Student class as below:
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package org.arpit.java2blog; public class Student { private int id; private String name; private String gender; private int age; public Student(int id, String name, String gender, int age) { super(); this.id = id; this.name = name; this.gender = gender; this.age = age; } public int getId() { return id; } public void setId(int id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public String getGender() { return gender; } public void setGender(String gender) { this.gender = gender; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } @Override public String toString() { return "Student [id=" + id + ", name=" + name + ", gender=" + gender + ", age=" + age + "]"; } } |
Lets say you have list of student objects in studentList and you need to filter all male students.
You can do it with the help of Stream with below code:
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// Filter all male students List maleStudents=studentList.stream() .filter(s-> s.getGender().equalsIgnoreCase("M") ) .collect(Collectors.toList()); System.out.println("Male students are :"+maleStudents); |
Here we have used stream‘s filter method to filter list and then collect the result to another list with Collectors.toList().
You can use stream’s filter method to filter list and use findAny and orElse method based on conditions.
For example:You want to filter Student with name John, if you do not find it in the list then return null.
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// Filer based on name Student student=studentList.stream() .filter(s-> s.getName().equalsIgnoreCase("John")) .findAny() .orElse(null); System.out.println("Student with Name john :"+student); |
Lets create a main class as below:
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package org.arpit.java2blog; import java.util.ArrayList; import java.util.List; import java.util.function.Predicate; import java.util.stream.Collectors; public class Java8StreamFilterExamples { public static void main(String[] args) { List studentList=createStudentList(); // Filter all male students List maleStudents=studentList.stream() .filter(s>s.getGender().equalsIgnoreCase("M")) .collect(Collectors.toList()); System.out.println("Male students are :"+maleStudents); // Filter based on name Student student=studentList.stream() .filter(s-> s.getName().equalsIgnoreCase("John")) .findAny() .orElse(null); System.out.println("Student with Name john :"+student); } public static List createStudentList() { List studentList=new ArrayList(); Student s1=new Student(1, "Arpit", "M", 19); Student s2=new Student(2, "John", "M", 17); Student s3=new Student(3, "Mary", "F", 14); Student s4=new Student(4, "Martin", "M", 21); Student s5=new Student(5, "Monica", "F", 16); Student s6=new Student(6, "Ally", "F", 20); studentList.add(s1); studentList.add(s2); studentList.add(s3); studentList.add(s4); studentList.add(s5); studentList.add(s6); return studentList; } } |
When you run above program, you will get below output:
Let me know if you need more examples for Stream‘s filter method.
