Valores únicos en un List

Para obtener valores únicos en un List<String> collection, pueden ocupar esto:

package Test;

import java.util.ArrayList;

import java.util.Arrays;

import java.util.HashSet;

import java.util.List;

public class UniqueValues {

public static void main(String[] args) {

      String[] words = 

{"juan", "pedro", "luis","juan", "pedro", "luis","juan", "pedro", "luis"};

           

List<String> oldList = Arrays.asList(words); 

List<String> uniqueList = new ArrayList<String>(

new HashSet<String>(oldList));

System.out.println("Resultado:");

for (String string : uniqueList) {

System.out.println("\t - " + string);

}

}

}

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Si lo quieren hacer en un objeto, se requiere implementar: hashCode() y equals() de la clase a usar:

package Test;

public class Element {

int id;

String name;

int age;

public Element(int id, String name, int age) {

super();

this.id = id;

this.name = name;

this.age = age;

}

/**

* @return the id

*/

public int getId() {

return id;

}

/**

* @param id

*            the id to set

*/

public void setId(int id) {

this.id = id;

}

/**

* @return the name

*/

public String getName() {

return name;

}

/**

* @param name

*            the name to set

*/

public void setName(String name) {

this.name = name;

}

/**

* @return the age

*/

public int getAge() {

return age;

}

/**

* @param age

*            the age to set

*/

public void setAge(int age) {

this.age = age;

}

@Override

public boolean equals(Object o) {

    if (o instanceof Element) {

        Element other = (Element) o;

        return this.id == other.getId();

    }

    return false;

}

@Override

public int hashCode() {

return this.id;

}

}

Y ocupan el mismo código para filtrar valores únicos:

package Test;

import java.util.ArrayList;

import java.util.Arrays;

import java.util.HashSet;

import java.util.List;

public class UniqueValues {

public static void main(String[] args) {

Element[] entities = new Element[9];

entities[0] = new Element (1, "A" ,5);

entities[1] = new Element (2, "B" ,5);

entities[2] = new Element (3, "C" ,5);

entities[3] = new Element (1, "A" ,5);

entities[4] = new Element (2, "B" ,5);

entities[5] = new Element (3, "C" ,5);

entities[6] = new Element (1, "A" ,5);

entities[7] = new Element (2, "B" ,5);

entities[8] = new Element (3, "C" ,5);

            

List<Element> uniqueList = 

new ArrayList<Element>(

new HashSet<Element>(

Arrays.asList(entities)));

System.out.println("Resultado:");

for (Element element : uniqueList) {

System.out.println("\t - " + element.getId());

}

}

}