This post demonstrates how to reuse Predicate @FunctionalInterface implementations to reduce duplicate codes in your applications.

java.util.function.Predicate

This functional interface has a number of default methods defined that can be used to extend existing Predicates Lambdas.

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 * Copyright (c) 2010, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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package java.util.function;

import java.util.Objects;

/**
 * Represents a predicate (boolean-valued function) of one argument.
 *
 * <p>This is a <a href="package-summary.html">functional interface</a>
 * whose functional method is {@link #test(Object)}.
 *
 * @param <T> the type of the input to the predicate
 *
 * @since 1.8
 */
@FunctionalInterface
public interface Predicate<T> {

    /**
     * Evaluates this predicate on the given argument.
     *
     * @param t the input argument
     * @return {@code true} if the input argument matches the predicate,
     * otherwise {@code false}
     */
    boolean test(T t);

    /**
     * Returns a composed predicate that represents a short-circuiting logical
     * AND of this predicate and another.  When evaluating the composed
     * predicate, if this predicate is {@code false}, then the {@code other}
     * predicate is not evaluated.
     *
     * <p>Any exceptions thrown during evaluation of either predicate are relayed
     * to the caller; if evaluation of this predicate throws an exception, the
     * {@code other} predicate will not be evaluated.
     *
     * @param other a predicate that will be logically-ANDed with this
     *              predicate
     * @return a composed predicate that represents the short-circuiting logical
     * AND of this predicate and the {@code other} predicate
     * @throws NullPointerException if other is null
     */
    default Predicate<T> and(Predicate<? super T> other) {
        Objects.requireNonNull(other);
        return (t) -> test(t) && other.test(t);
    }

    /**
     * Returns a predicate that represents the logical negation of this
     * predicate.
     *
     * @return a predicate that represents the logical negation of this
     * predicate
     */
    default Predicate<T> negate() {
        return (t) -> !test(t);
    }

    /**
     * Returns a composed predicate that represents a short-circuiting logical
     * OR of this predicate and another.  When evaluating the composed
     * predicate, if this predicate is {@code true}, then the {@code other}
     * predicate is not evaluated.
     *
     * <p>Any exceptions thrown during evaluation of either predicate are relayed
     * to the caller; if evaluation of this predicate throws an exception, the
     * {@code other} predicate will not be evaluated.
     *
     * @param other a predicate that will be logically-ORed with this
     *              predicate
     * @return a composed predicate that represents the short-circuiting logical
     * OR of this predicate and the {@code other} predicate
     * @throws NullPointerException if other is null
     */
    default Predicate<T> or(Predicate<? super T> other) {
        Objects.requireNonNull(other);
        return (t) -> test(t) || other.test(t);
    }

    /**
     * Returns a predicate that tests if two arguments are equal according
     * to {@link Objects#equals(Object, Object)}.
     *
     * @param <T> the type of arguments to the predicate
     * @param targetRef the object reference with which to compare for equality,
     *               which may be {@code null}
     * @return a predicate that tests if two arguments are equal according
     * to {@link Objects#equals(Object, Object)}
     */
    static <T> Predicate<T> isEqual(Object targetRef) {
        return (null == targetRef)
                ? Objects::isNull
                : object -> targetRef.equals(object);
    }
}

67	default Predicate<T> and(Predicate<? super T> other) {

Example Codes

PersonBean

First we create a class called PersonBean that represents a person and has the following few fields.

public class PersonBean {
	
	private int age;
	private String name;
	private String countryCode;
	private String state;
	
	public PersonBean(int age, String name, String countryCode, String state) {
		super();
		this.age = age;
		this.name = name;
		this.countryCode = countryCode;
		this.state = state;
	}
	
	public int getAge() {
		return age;
	}
	public void setAge(int age) {
		this.age = age;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public String getCountryCode() {
		return countryCode;
	}
	public void setCountryCode(String countryCode) {
		this.countryCode = countryCode;
	}
	public String getState() {
		return state;
	}
	public void setState(String state) {
		this.state = state;
	}

	@Override
	public String toString() {
		return "PersonBean [age=" + age + ", name=" + name + ", countryCode=" + countryCode + ", state=" + state + "]";
	}
}

public class PersonBean {

private int age;

private String name;

private String countryCode;

private String state;

public PersonBean(int age, String name, String countryCode, String state) {

super();

this.age = age;

this.name = name;

this.countryCode = countryCode;

this.state = state;

}

public int getAge() {

return age;

}

public void setAge(int age) {

this.age = age;

}

public String getName() {

return name;

}

public void setName(String name) {

this.name = name;

}

public String getCountryCode() {

return countryCode;

}

public void setCountryCode(String countryCode) {

this.countryCode = countryCode;

}

public String getState() {

return state;

}

public void setState(String state) {

this.state = state;

}

@Override

public String toString() {

return "PersonBean [age=" + age + ", name=" + name + ", countryCode=" + countryCode + ", state=" + state + "]";

}

Main class

This is our main class.

import java.util.List;
import java.util.function.Predicate;
import java.util.stream.Collectors;
import java.util.stream.Stream;

public class CombinePredicateFunction {

	public static void main(String[] args) {
		List<PersonBean> personList = Stream.of(
				new PersonBean(12, "Lance", "MY", "MY-14"), 
				new PersonBean(24, "Martin", "MY", "MY-06"),
				new PersonBean(25, "Luke", "MY", "MY-10"),
				new PersonBean(10, "AShley", "US", "GA"),
				new PersonBean(30, "Kurt", "US", "CA")).collect(Collectors.toList());
		
		Predicate<PersonBean> usOnly = (p) -> p.getCountryCode().equals("US");
		Predicate<PersonBean> stateCAOnly = (p) -> p.getState().equals("GA");
		
		// Display all persons from US (country code only)
		System.out.println(personList.stream().filter(usOnly).collect(Collectors.toList()));
		
		// Create a new predicate from the combination of usOnly and stateCAOnly
		Predicate<PersonBean> usAndCa = usOnly.and(stateCAOnly);
		System.out.println(personList.stream().filter(usAndCa).collect(Collectors.toList()));
		
		// Original predicate not modified
		System.out.println(personList.stream().filter(usOnly).collect(Collectors.toList()));
		
		Predicate<PersonBean> myOnly = (p) -> p.getCountryCode().equals("MY");
		Predicate<PersonBean> legalAge = (p) -> p.getAge() >= 18;
		
		// List all persons from Malaysia
		System.out.println(personList.stream().filter(myOnly).collect(Collectors.toList()));
		
		Predicate<PersonBean> malaysianLegalAge = myOnly.and(legalAge);
		
		// List all persons from Malaysia who are of legal age
		System.out.println(personList.stream().filter(malaysianLegalAge).collect(Collectors.toList()));
	}
}

import java.util.List;

import java.util.function.Predicate;

import java.util.stream.Collectors;

import java.util.stream.Stream;

public class CombinePredicateFunction {

public static void main(String[] args) {

List<PersonBean> personList = Stream.of(

new PersonBean(12, "Lance", "MY", "MY-14"),

new PersonBean(24, "Martin", "MY", "MY-06"),

new PersonBean(25, "Luke", "MY", "MY-10"),

new PersonBean(10, "AShley", "US", "GA"),

new PersonBean(30, "Kurt", "US", "CA")).collect(Collectors.toList());

Predicate<PersonBean> usOnly = (p) -> p.getCountryCode().equals("US");

Predicate<PersonBean> stateCAOnly = (p) -> p.getState().equals("GA");

// Display all persons from US (country code only)

System.out.println(personList.stream().filter(usOnly).collect(Collectors.toList()));

// Create a new predicate from the combination of usOnly and stateCAOnly

Predicate<PersonBean> usAndCa = usOnly.and(stateCAOnly);

System.out.println(personList.stream().filter(usAndCa).collect(Collectors.toList()));

// Original predicate not modified

System.out.println(personList.stream().filter(usOnly).collect(Collectors.toList()));

Predicate<PersonBean> myOnly = (p) -> p.getCountryCode().equals("MY");

Predicate<PersonBean> legalAge = (p) -> p.getAge() >= 18;

// List all persons from Malaysia

System.out.println(personList.stream().filter(myOnly).collect(Collectors.toList()));

Predicate<PersonBean> malaysianLegalAge = myOnly.and(legalAge);

// List all persons from Malaysia who are of legal age

System.out.println(personList.stream().filter(malaysianLegalAge).collect(Collectors.toList()));

}

Outputs:

[PersonBean [age=10, name=AShley, countryCode=US, state=GA], PersonBean [age=30, name=Kurt, countryCode=US, state=CA]]
[PersonBean [age=10, name=AShley, countryCode=US, state=GA]]
[PersonBean [age=10, name=AShley, countryCode=US, state=GA], PersonBean [age=30, name=Kurt, countryCode=US, state=CA]]
[PersonBean [age=12, name=Lance, countryCode=MY, state=MY-14], PersonBean [age=24, name=Martin, countryCode=MY, state=MY-06], PersonBean [age=25, name=Luke, countryCode=MY, state=MY-10]]
[PersonBean [age=24, name=Martin, countryCode=MY, state=MY-06], PersonBean [age=25, name=Luke, countryCode=MY, state=MY-10]]

[PersonBean [age=10, name=AShley, countryCode=US, state=GA], PersonBean [age=30, name=Kurt, countryCode=US, state=CA]]

[PersonBean [age=10, name=AShley, countryCode=US, state=GA]]

[PersonBean [age=10, name=AShley, countryCode=US, state=GA], PersonBean [age=30, name=Kurt, countryCode=US, state=CA]]

[PersonBean [age=12, name=Lance, countryCode=MY, state=MY-14], PersonBean [age=24, name=Martin, countryCode=MY, state=MY-06], PersonBean [age=25, name=Luke, countryCode=MY, state=MY-10]]