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Function Interface in Java

Java 8 Predicate with Examples

Last Updated : 21 Oct, 2022

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A Functional Interface is an Interface which allows only one Abstract method within the Interface scope. There are some predefined functional interface in Java like Predicate, consumer, supplier etc. The return type of a Lambda function (introduced in JDK 1.8) is a also functional interface.

The Functional Interface PREDICATE is defined in the java.util.function package. It improves manageability of code, helps in unit-testing them separately, and contain some methods like:

isEqual(Object targetRef) : Returns a predicate that tests if two arguments are equal according to Objects.equals(Object, Object).

static  Predicate isEqual(Object targetRef)  Returns a predicate that tests if two arguments are   equal according to Objects.equals(Object, Object).  T : the type of arguments to the predicate  Parameters:  targetRef : the object reference with which to   compare for equality, which may be null  Returns: a predicate that tests if two arguments   are equal according to Objects.equals(Object, Object)

and(Predicate other) : Returns a composed predicate that represents a short-circuiting logical AND of this predicate and another.

default Predicate and(Predicate other)  Returns a composed predicate that represents a   short-circuiting logical AND of this predicate and another.  Parameters:  other: a predicate that will be logically-ANDed with this predicate  Returns : a composed predicate that represents the short-circuiting   logical AND of this predicate and the other predicate  Throws: NullPointerException - if other is null

negate() : Returns a predicate that represents the logical negation of this predicate.

default Predicate negate()  Returns:a predicate that represents the logical   negation of this predicate

or(Predicate other) : Returns a composed predicate that represents a short-circuiting logical OR of this predicate and another.

default Predicate or(Predicate other)  Parameters:  other : a predicate that will be logically-ORed with this predicate  Returns:  a composed predicate that represents the short-circuiting   logical OR of this predicate and the other predicate  Throws : NullPointerException - if other is null

test(T t) : Evaluates this predicate on the given argument.boolean test(T t)

test(T t)   Parameters:  t - the input argument  Returns:  true if the input argument matches the predicate, otherwise false

Examples

Example 1: Simple Predicate

Java

   // Java program to illustrate Simple Predicate 
  
import java.util.function.Predicate; 
public class PredicateInterfaceExample1 { 
    public static void main(String[] args) 
    { 
        // Creating predicate 
        Predicate<Integer> lesserthan = i -> (i < 18);  
  
        // Calling Predicate method 
        System.out.println(lesserthan.test(10));  
    } 
} 
 
  

Output:

  True

Example 2: Predicate Chaining

Java

   // Java program to illustrate Predicate Chaining 
  
import java.util.function.Predicate; 
public class PredicateInterfaceExample2 { 
    public static void main(String[] args) 
    { 
        Predicate<Integer> greaterThanTen = (i) -> i > 10; 
  
        // Creating predicate 
        Predicate<Integer> lowerThanTwenty = (i) -> i < 20;  
        boolean result = greaterThanTen.and(lowerThanTwenty).test(15); 
        System.out.println(result); 
  
        // Calling Predicate method 
        boolean result2 = greaterThanTen.and(lowerThanTwenty).negate().test(15); 
        System.out.println(result2); 
    } 
} 
 
  

Output:

  True  False

Example 3: Predicate in to Function

Java

   // Java program to illustrate  
// passing Predicate into function 
  
import java.util.function.Predicate; 
class PredicateInterfaceExample3 { 
    static void pred(int number, Predicate<Integer> predicate) 
    { 
        if (predicate.test(number)) { 
            System.out.println("Number " + number); 
        } 
    } 
    public static void main(String[] args) 
    { 
        pred(10, (i) -> i > 7); 
    } 
} 
 
  

Output:

  Number 10

Example 4: Predicate OR

Java

   // Java program to illustrate OR Predicate 
  
import java.util.function.Predicate; 
class PredicateInterfaceExample4 { 
    public static Predicate<String> hasLengthOf10 = new Predicate<String>() { 
        @Override
        public boolean test(String t) 
        { 
            return t.length() > 10; 
        } 
    }; 
  
    public static void predicate_or() 
    { 
  
        Predicate<String> containsLetterA = p -> p.contains("A"); 
        String containsA = "And"; 
        boolean outcome = hasLengthOf10.or(containsLetterA).test(containsA); 
        System.out.println(outcome); 
    } 
    public static void main(String[] args) 
    { 
        predicate_or(); 
    } 
} 
 
  

Output:

  True

Example 5: Predicate AND

Java

   // Java program to illustrate AND Predicate 
  
import java.util.function.Predicate; 
import java.util.Objects; 
  
class PredicateInterfaceExample5 { 
    public static Predicate<String> hasLengthOf10 = new Predicate<String>() { 
        @Override
        public boolean test(String t) 
        { 
            return t.length() > 10; 
        } 
    }; 
  
    public static void predicate_and() 
    { 
        Predicate<String> nonNullPredicate = Objects::nonNull; 
  
        String nullString = null; 
  
        boolean outcome = nonNullPredicate.and(hasLengthOf10).test(nullString); 
        System.out.println(outcome); 
  
        String lengthGTThan10 = "Welcome to the machine"; 
        boolean outcome2 = nonNullPredicate.and(hasLengthOf10). 
        test(lengthGTThan10); 
        System.out.println(outcome2); 
    } 
    public static void main(String[] args) 
    { 
        predicate_and(); 
    } 
} 
 
  

Output:

  False  True

Example 6: Predicate negate()

Java

   // Java program to illustrate  
// negate Predicate 
  
import java.util.function.Predicate; 
class PredicateInterfaceExample6 { 
    public static Predicate<String> hasLengthOf10 = new Predicate<String>() { 
        @Override
        public boolean test(String t) 
        { 
            return t.length() > 10; 
        } 
    }; 
  
    public static void predicate_negate() 
    { 
  
        String lengthGTThan10 = "Thunderstruck is a 2012 children's "
                                + "film starring Kevin Durant"; 
  
        boolean outcome = hasLengthOf10.negate().test(lengthGTThan10); 
        System.out.println(outcome); 
    } 
    public static void main(String[] args) 
    { 
        predicate_negate(); 
    } 
} 
 
  

Output:

  False

Example 7: Predicate in Collection

Java

   // Java program to demonstrate working of predicates 
// on collection. The program finds all admins in an 
// arrayList of users. 
import java.util.function.Predicate; 
import java.util.*; 
class User 
{ 
    String name, role; 
    User(String a, String b) { 
        name = a; 
        role = b; 
    } 
    String getRole() { return role; } 
    String getName() { return name; }     
    public String toString() { 
       return "User Name : " + name + ", Role :" + role; 
    } 
  
    public static void main(String args[]) 
    {       
        List<User> users = new ArrayList<User>(); 
        users.add(new User("John", "admin")); 
        users.add(new User("Peter", "member")); 
        List admins = process(users, (User u) -> u.getRole().equals("admin")); 
        System.out.println(admins); 
    } 
  
    public static List<User> process(List<User> users,  
                            Predicate<User> predicate) 
    { 
        List<User> result = new ArrayList<User>(); 
        for (User user: users)         
            if (predicate.test(user))             
                result.add(user); 
        return result; 
    } 
} 
 
  

Output:

[User Name : John, Role :admin]

The same functionality can also be achieved by using Stream API
and lambda functions offered since JDK 1.8 on top of the Collections API.

The Stream API allows "streaming" of collections for dynamic processing. Streams allow concurrent and parallel computation on data (using internal iterations), to support database-like operations such as grouping and filtering the data (similar to GROUP BY and WHERE clause in SQL). This allows the developers to focus on "what data is needed" instead of "how data is needed" since streaming hides the details of the implementation and provides the result. This is done by providing predicates as inputs to functions operating at runtime upon the streams of collections. In the following example, we illustrate how Stream API can be used along with predicates to filter the collections of data as achieved in Example 7.

Java

   // Java program to demonstrate working of predicates 
// on collection. The program finds all admins in an 
// arrayList of users. 
import java.util.function.Predicate; 
import java.util.*; 
import java.util.stream.Collectors; 
import java.util.stream.Stream; 
  
class User 
{ 
    String name, role; 
    User(String a, String b) { 
        name = a; 
        role = b; 
    } 
    String getRole() { return role; } 
    String getName() { return name; }  
    public String toString() { 
    return "User Name : " + name + ", 
    Role :" + role; 
    } 
  
    public static void main(String args[]) 
    {  
        List<User> users =  
            new ArrayList<User>(); 
        users.add(new User("John", "admin")); 
        users.add(new User("Peter", "member")); 
          
    // This line uses Predicates to filter 
    // out the list of users with the role "admin". 
    // List admins = process(users, (User u) ->  
    // u.getRole().equals("admin")); 
  
    // Replacing it with the following line  
    // using Stream API and lambda functions  
    // produces the same output 
      
    // the input to the filter() is a lambda  
    // expression that returns a predicate: a  
    // boolean value for each user encountered  
    // (true if admin, false otherwise) 
    List admins = users.stream() 
    .filter((user) -> user.getRole().equals("admin")) 
    .collect(Collectors.toList()); 
          
    System.out.println(admins); 
    } 
} 
 
  

Output:

[User Name : John, Role :admin]

Function Interface in Java

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Optional orElse() method in Java with examples

The orElse() method of java.util.Optional class in Java is used to get the value of this Optional instance, if present. If there is no value present in this Optional instance, then this method returns the specified value. Syntax: public T orElse(T value) Parameters: This method accepts value as a pa

2 min read
Optional ifPresentOrElse() method in Java with examples

The ifPresentOrElse(Consumer, Runnable) method of java.util.Optional class helps us to perform the specified Consumer action the value of this Optional object. If a value is not present in this Optional, then this method performs the given empty-based Runnable emptyAction, passed as the second param

2 min read
Optional orElseGet() Method in Java

The orElseGet() method of java.util.Optional class in Java is used to get the value of this Optional instance if present. If there is no value present in this Optional instance, then this method returns the value generated from the specified supplier. Syntax of orElseGet() Methodpublic T orElseGet(S

2 min read
Optional filter() method in Java with examples

The filter() method of java.util.Optional class in Java is used to filter the value of this Optional instance by matching it with the given Predicate, and then return the filtered Optional instance. If there is no value present in this Optional instance, then this method returns an empty Optional in

2 min read
Optional empty() method in Java with examples

The empty() method of java.util.Optional class in Java is used to get an empty instance of this Optional class. This instance do not contain any value. Syntax: public static <T> Optional<T> empty() Parameters: This method accepts nothing. Return value: This method returns an empty instan

1 min read
Optional hashCode() method in Java with examples

The hashCode() method of java.util.Optional class in Java is used to get the hashCode value of this Optional instance. If there is no value present in this Optional instance, then this method returns 0. Syntax: public int hashCode() Parameter: This method do not accepts any parameter. Return Value:

1 min read
Optional toString() method in Java with examples

The toString() method of java.util.Optional class in Java is used to get the string representation of this Optional instance. Syntax: public String toString() Parameters: This method accepts nothing. Return value: This method returns the string representation of this Optional instance. Below program

1 min read
Optional equals() method in Java with Examples

The equals() method of java.util.Optional class in Java is used to check for equality of this Optional with the specified Optional. This method takes an Optional instance and compares it with this Optional and returns a boolean value representing the same. Syntax: public boolean equals(Object obj) P

2 min read

Date/Time API

New Date-Time API in Java 8

New date-time API is introduced in Java 8 to overcome the following drawbacks of old date-time API : Not thread safe : Unlike old java.util.Date which is not thread safe the new date-time API is immutable and doesn't have setter methods.Less operations : In old API there are only few date operations

6 min read
java.time.LocalDate Class in Java

Java is the most popular programming language and widely used programming language. Java is used in all kind of application like as mobile application, desktop application, web application. In this Java java.time.LocalDate class is imported which represents to display the current date. java.time: It

4 min read
java.time.LocalTime Class in Java

Java is the most popular programming language and widely used programming language. Java is used in all kinds of applications like mobile applications, desktop applications, web applications. As in Java, java.time.LocalTime class represents time, which is viewed as hour-minute-second. This class is

5 min read
java.time.LocalDateTime Class in Java

java.time.LocalDateTime class, introduced in Java 8, represents a local date-time object without timezone information. The LocalDateTime class in Java is an immutable date-time object that represents a date in the yyyy-MM-dd-HH-mm-ss.zzz format. It implements the ChronoLocalDateTime interface and in

4 min read
java.time.MonthDay Class in Java

Java is the most popular programming language and widely used programming language. Java is used in all kinds of applications like mobile applications, desktop applications, web applications. The java.time.MonthDay class represents a combination of month and day of the month, and it is immutable. ja

3 min read
java.time.OffsetTime Class in Java

Java OffsetTime class is an immutable date-time object that represents a time, often viewed as hour-minute-second offset. OffsetTime class represents a time with an offset from UTC/Greenwich in the ISO-8601 calendar system, such as 18:30:45+08:00, often viewed as an hour-minute-second-offset. This c

7 min read
java.time.OffsetDateTime Class in Java

Java is the most popular programming language and widely used programming language. Java is used in all kind of application like mobile application, desktop application, web application. In this Java java.time.OffsetDate, Time class is imported which is an immutable representation of a date-time wit

4 min read
java.time.Clock Class in Java

Java Clock class is present in java.time package. It was introduced in Java 8 and provides access to current instant, date, and time using a time zone. The use of the Clock class is not mandatory because all date-time classes also have a now() method that uses the system clock in the default time zo

3 min read
java.time.ZonedDateTime Class in Java

ZonedDateTime is an immutable object representing a date-time along with the time zone. This class stores all date and time fields.This class stores time to a precision of nanoseconds and a time-zone, with a zone Offset used to handle local date-times. For example, the value â€œ2nd October 2011 at 14:

8 min read
java.time.ZoneId Class in Java

A ZoneId is used to identify the rules that used to convert between a LocalDateTime and an Instant of time. The actual rules, describing when and the way the offset changes, are defined by ZoneRules. This class is just an ID wont to obtain the underlying rules. The given approach has opted because t

3 min read

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