demo2.java

package Advances.CollectionDemo;

/** Collection demo 2 */

// https://www.youtube.com/watch?v=WO-54GprY0M&list=PLmOn9nNkQxJH0qBIrtV6otI0Ep4o2q67A&index=519
// https://www.youtube.com/watch?v=hyj5uygJyLU&list=PLmOn9nNkQxJH0qBIrtV6otI0Ep4o2q67A&index=520
// https://www.youtube.com/watch?v=hyj5uygJyLU&list=PLmOn9nNkQxJH0qBIrtV6otI0Ep4o2q67A&index=520

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import org.junit.jupiter.api.Test;

/**
 * Collection interface method demo
 *
 * <p>1) if we add user-defined-class obj to Collection -> we need to override obj class' equals()
 * method
 */
public class demo2 {

  @Test
  public void test1() {

    /** contains */
    Collection col1 = new ArrayList();
    col1.add(123);
    col1.add(456);
    col1.add("yooooo");
    col1.add("kate");
    Person p = new Person("tom", 20);
    col1.add(p);
    col1.add(new Person("kyo", 19));

    System.out.println(col1.contains(123));
    System.out.println(col1.contains(000));

    // Contains(Object obj) : check if current collections has obj
    // *** Will use obj class' `equals()` when check above
    // --> if needed, we can override obj class' `equals()`
    System.out.println(col1.contains("kate")); // true

    System.out.println(
        col1.contains(
            new Person(
                "tom", 20))); // false (true : after override equals methods in Person class )
    System.out.println(col1.contains(p)); // true

    System.out.println(
        col1.contains(
            new Person(
                "kyo", 19))); // false (true : after override equals methods in Person class )
  }

  @Test
  public void test2() {

    /** containsAll */
    Collection col1 = Arrays.asList(123, 456);
    System.out.println(col1.containsAll(col1)); // true
  }

  @Test
  public void test3() {

    /** remove */
    Collection col1 = new ArrayList();
    col1.add(123);
    col1.add(456);
    col1.add("yooooo");
    col1.add("kate");
    col1.add(new Person("kyo", 19));

    System.out.println(col1.remove(123));
    System.out.println(col1.remove(new Person("terry", 10)));
  }

  @Test
  public void test4() {

    /** removeAll */
    Collection col1 = Arrays.asList(123, 456);
    // col1.removeAll(col1);

    System.out.println(col1);
  }

  @Test
  public void test5() {

    /** retainAll : get overlap within collections */
    Collection col1 = new ArrayList();
    col1.add(123);
    col1.add(456);
    col1.add("yooooo");

    Collection col2 = Arrays.asList(123, 789, 000);
    col1.retainAll(col2);

    System.out.println(col1);
  }

  @Test
  public void test6() {

    /** equals(Object obj) : check if two collections are equal */
    Collection col1 = new ArrayList();
    col1.add(123);
    col1.add(456);
    col1.add("yooooo");

    Collection col2 = new ArrayList();
    col2.add(123);
    col2.add(456);
    col2.add("yooooo");

    System.out.println(col1.equals(col2)); // true
  }

  @Test
  public void test7() {

    /** remove(Object obj) : remove obj element from current collection */
    Collection col1 = new ArrayList();
    col1.add(123);
    col1.add(456);
    col1.add(789);
    col1.add("yooooo");
    col1.add("kate");
    col1.add(new Person("kyo", 19));

    col1.remove(123);
    System.out.println(col1);

    System.out.println("-----------------");

    col1.remove(new Person("kyo", 19));
    System.out.println(col1);

    System.out.println("-----------------");

    /** removeAll(collection col1) : remove all elements from current collection */
    Collection col2 = Arrays.asList(456, 789);
    col1.removeAll(col2);
    System.out.println(col1);
  }

  @Test
  public void test8() {

    /** retainAll : get overlap over 2 collections (in-place) */
    Collection col1 = new ArrayList();
    col1.add(123);
    col1.add(456);
    col1.add(789);
    col1.add("yooooo");
    col1.add("kate");
    col1.add(new Person("kyo", 19));

    Collection col2 = Arrays.asList(456, 789);

    col1.retainAll(col2);

    System.out.println(col1);
  }

  @Test
  public void test9() {

    /** equals (Object obj) */
    Collection col1 = new ArrayList();
    col1.add(123);
    col1.add(456);
    col1.add(789);
    col1.add("yooooo");
    col1.add("kate");
    col1.add(new Person("kyo", 19));

    Collection col2 = Arrays.asList(456, 789);
    Collection col3 = Arrays.asList(456, 789);
    Collection col4 = Arrays.asList(789, 456);

    System.out.println(col1.equals(col2)); // false
    System.out.println(col2.equals(col3)); // true
    System.out.println(col3.equals(col4)); // false !! (ArrayList is ordering)
  }
}