Adding collection utils guide
Adding Apache Commons 4 Collection Utils guide
This commit is contained in:
Himanshu Mantri
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<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
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<modelVersion>4.0.0</modelVersion>
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<groupId>baeldung</groupId>
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<artifactId>collectionutils</artifactId>
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<version>0.0.1-SNAPSHOT</version>
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<name>collectionutils-guide</name>
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<description>A guide to Apache Commons CollectionUtils</description>
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<properties>
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<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
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<project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
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<java.version>1.8</java.version>
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</properties>
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<dependencies>
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<!-- https://mvnrepository.com/artifact/org.apache.commons/commons-collections4 -->
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<dependency>
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<groupId>org.apache.commons</groupId>
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<artifactId>commons-collections4</artifactId>
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<version>4.0</version>
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</dependency>
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<!-- https://mvnrepository.com/artifact/junit/junit -->
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<dependency>
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<groupId>junit</groupId>
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<artifactId>junit</artifactId>
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<version>4.12</version>
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<scope>test</scope>
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</dependency>
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</dependencies>
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</project>
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package com.baeldung.collectionutilsguide.model;
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public class Address {
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String locality;
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String city;
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String zip;
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public String getLocality() {
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return locality;
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}
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public void setLocality(String locality) {
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this.locality = locality;
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}
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public String getCity() {
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return city;
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}
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public void setCity(String city) {
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this.city = city;
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}
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public String getZip() {
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return zip;
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}
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public void setZip(String zip) {
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this.zip = zip;
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}
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@Override
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public String toString() {
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StringBuilder builder = new StringBuilder();
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builder.append("Address [locality=").append(locality).append(", city=").append(city).append(", zip=").append(zip).append("]");
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return builder.toString();
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}
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public Address(String locality, String city, String zip) {
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super();
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this.locality = locality;
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this.city = city;
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this.zip = zip;
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}
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}
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package com.baeldung.collectionutilsguide.model;
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public class Customer implements Comparable<Customer> {
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Integer id;
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String name;
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Long phone;
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String locality;
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String city;
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String zip;
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public Integer getId() {
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return id;
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}
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public void setId(Integer id) {
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this.id = id;
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}
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public String getName() {
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return name;
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}
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public void setName(String name) {
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this.name = name;
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}
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public Long getPhone() {
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return phone;
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}
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public void setPhone(Long phone) {
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this.phone = phone;
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}
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public String getLocality() {
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return locality;
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}
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public void setLocality(String locality) {
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this.locality = locality;
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}
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public String getCity() {
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return city;
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}
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public void setCity(String city) {
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this.city = city;
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}
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public String getZip() {
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return zip;
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}
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public void setZip(String zip) {
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this.zip = zip;
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}
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public Customer(Integer id, String name, Long phone, String locality, String city, String zip) {
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super();
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this.id = id;
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this.name = name;
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this.phone = phone;
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this.locality = locality;
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this.city = city;
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this.zip = zip;
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}
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public Customer(Integer id, String name, Long phone) {
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super();
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this.id = id;
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this.name = name;
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this.phone = phone;
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}
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public Customer(String name) {
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super();
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this.name = name;
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}
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@Override
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public int hashCode() {
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final int prime = 31;
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int result = 1;
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result = prime * result + ((name == null) ? 0 : name.hashCode());
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return result;
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}
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@Override
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public boolean equals(Object obj) {
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if (this == obj)
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return true;
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if (obj == null)
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return false;
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if (getClass() != obj.getClass())
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return false;
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Customer other = (Customer) obj;
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if (name == null) {
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if (other.name != null)
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return false;
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} else if (!name.equals(other.name))
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return false;
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return true;
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}
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public int compareTo(Customer o) {
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return this.name.compareTo(o.getName());
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}
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@Override
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public String toString() {
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StringBuilder builder = new StringBuilder();
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builder.append("Customer [id=").append(id).append(", name=").append(name).append(", phone=").append(phone).append("]");
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return builder.toString();
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}
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}
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package collectionutils;
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import static org.junit.Assert.assertFalse;
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import static org.junit.Assert.assertTrue;
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import java.util.ArrayList;
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import java.util.Arrays;
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import java.util.Collection;
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import java.util.LinkedList;
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import java.util.List;
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import org.apache.commons.collections4.Closure;
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import org.apache.commons.collections4.CollectionUtils;
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import org.apache.commons.collections4.Predicate;
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import org.apache.commons.collections4.Transformer;
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import org.junit.Test;
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import com.baeldung.collectionutilsguide.model.Address;
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import com.baeldung.collectionutilsguide.model.Customer;
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public class CollectionUtilsGuideTest {
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Customer customer1 = new Customer(1, "Daniel", 123456l, "locality1", "city1", "1234");
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Customer customer2 = new Customer(2, "Fredrik", 234567l, "locality2", "city2", "2345");
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Customer customer3 = new Customer(3, "Kyle", 345678l, "locality3", "city3", "3456");
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Customer customer4 = new Customer(4, "Bob", 456789l, "locality4", "city4", "4567");
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Customer customer5 = new Customer(5, "Cat", 567890l, "locality5", "city5", "5678");
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Customer customer6 = new Customer(6, "John", 678901l, "locality6", "city6", "6789");
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List<Customer> list1 = Arrays.asList(customer1, customer2, customer3);
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List<Customer> list2 = Arrays.asList(customer4, customer5, customer6);
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List<Customer> list3 = Arrays.asList(customer1, customer2);
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List<Customer> linkedList1 = new LinkedList<Customer>(list1);
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@Test
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public void givenList_WhenAddIgnoreNull_thenNoNullAdded() {
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List<String> list = Arrays.asList("x", "y", "z");
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CollectionUtils.addIgnoreNull(list, null);
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assertFalse(list.contains(null));
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}
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@Test
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public void givenTwoSortedLists_WhenCollated_thenSorted() {
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List<Customer> sortedList = CollectionUtils.collate(list1, list2);
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assertTrue(sortedList.get(0).getName().equals("Bob"));
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assertTrue(sortedList.get(2).getName().equals("Daniel"));
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}
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@Test
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public void givenListOfCustomers_whenTransformed_thenListOfAddress() {
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Collection<Address> addressCol = CollectionUtils.collect(list1, new Transformer<Customer, Address>() {
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public Address transform(Customer customer) {
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return new Address(customer.getLocality(), customer.getCity(), customer.getZip());
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}
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});
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List<Address> addressList = new ArrayList<Address>(addressCol);
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assertTrue(addressList.size() == 3);
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assertTrue(addressList.get(0).getLocality().equals("locality1"));
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}
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@Test
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public void givenCustomerList_WhenCountMatches_thenCorrect() {
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int result = CollectionUtils.countMatches(list1, new Predicate<Customer>() {
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public boolean evaluate(Customer customer) {
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return Arrays.asList("Daniel","Kyle").contains(customer.getName());
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}
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});
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assertTrue(result == 2);
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}
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@Test
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public void givenCustomerList_WhenFiltered_thenCorrectSize() {
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boolean isModified = CollectionUtils.filter(linkedList1, new Predicate<Customer>() {
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public boolean evaluate(Customer customer) {
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return Arrays.asList("Daniel","Kyle").contains(customer.getName());
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}
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});
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//filterInverse does the opposite. It removes the element from the list if the Predicate returns true
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//select and selectRejected work the same way except that they do not remove elements from the given collection and return a new collection
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assertTrue(isModified && linkedList1.size() == 2);
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}
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@Test
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public void givenCustomerList_WhenForAllDoSetNameNull_thenNameNull() {
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CollectionUtils.forAllDo(list1, new Closure<Customer>() {
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public void execute(Customer customer) {
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customer.setName(null);
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}
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});
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// forAllButLast does the same except for the last element in the collection
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assertTrue(list1.get(0).getName() == null);
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}
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@Test
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public void givenEmptyList_WhenCheckedIsEmpty_thenTrue() {
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List<Customer> emptyList = new ArrayList<Customer>();
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List<Customer> nullList = null;
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//Very handy at times where we want to check if a collection is not null and not empty too.
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//isNotEmpty does the opposite. Handy because using ! operator on isEmpty makes it missable while reading
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assertTrue(CollectionUtils.isEmpty(emptyList));
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assertTrue(CollectionUtils.isEmpty(nullList));
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}
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@Test
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public void givenCustomerListAndASubcollection_WhenChecked_thenTrue() {
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assertTrue(CollectionUtils.isSubCollection(list3, list1));
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}
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@Test
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public void givenTwoLists_WhenIntersected_thenCheckSize() {
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Collection<Customer> intersection = CollectionUtils.intersection(list1, list3);
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assertTrue(intersection.size() == 2);
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}
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@Test
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public void givenTwoLists_WhenSubtracted_thenCheckElementNotPresentInA() {
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Collection<Customer> result = CollectionUtils.subtract(list1, list3);
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assertFalse(result.contains(customer1));
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}
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@Test
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public void givenTwoLists_WhenUnioned_thenCheckElementPresentInResult() {
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Collection<Customer> union = CollectionUtils.union(list1, list2);
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assertTrue(union.contains(customer1));
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assertTrue(union.contains(customer4));
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}
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}
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