Handling null references - Java Object Oriented Design

Java examples for Object Oriented Design:Objects Utility

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Description

Handling null references

Demo Code

import java.util.ArrayList;
import java.util.Collections;
import java.util.ListIterator;
import java.util.Objects;

class Item {/*from   ww w  .j  a  v a 2 s  . co m*/
  private String name;
  private int partNumber;

  public Item() {
    this("Widget", 0);
  }

  public Item(String name, int partNumber) {
    this.name = Objects.requireNonNull(name);
    this.partNumber = partNumber;
  }

  public String getName() {
    return name;
  }

  public void setName(String name) {
    this.name = Objects.requireNonNull(name);
  }

  public int getPartNumber() {
    return partNumber;
  }

  public void setPartNumber(int partNumber) {
    this.partNumber = partNumber;
  }

  @Override
  public boolean equals(Object obj) {
    if (obj == null) {
      return false;
    }
    if (getClass() != obj.getClass()) {
      return false;
    }
    final Item other = (Item) obj;
    if (!Objects.equals(this.name, other.name)) {
      return false;
    }
    if (this.partNumber != other.partNumber) {
      return false;
    }
    return true;
  }

  @Override
  public int hashCode() {
    int hash = 7;
    hash = 47 * hash + Objects.hashCode(this.name);
    hash = 47 * hash + this.partNumber;
    return hash;
  }

  @Override
  public String toString() {
    return name + " - " + partNumber;
  }

}

public class Main {

  public static void main(String[] args) {
    Item item1 = new Item("Eraser", 2200);
    Item item2 = new Item("Eraser", 2200);
    Item item3 = new Item("Pencil", 1100);
    Item item4 = null;

    System.out.println("item1 equals item1: " + item1.equals(item1));
    System.out.println("item1 equals item2: " + item1.equals(item2));
    System.out.println("item1 equals item3: " + item1.equals(item3));
    System.out.println("item1 equals item4: " + item1.equals(item4));

    item2.setName(null);
    System.out.println("item1 equals item2: " + item1.equals(item2));

    // Additional Objects class methods
    item4 = null;
    System.out.println("toString: " + Objects.toString(item4));
    System.out.println("toString: " + Objects.toString(item4, "Item is null"));

    // Using empty iterators to avoid null pointer exceptions
    ListIterator<String> list = returnEmptyListIterator();
    while (list.hasNext()) {
      String item = list.next();
      System.out.println(item);
    }
  }

  // Using empty iterators to avoid null pointer exceptions
  public static ListIterator<String> returnEmptyListIterator() {
    boolean someConditionMet = false;
    if (someConditionMet) {
      ArrayList<String> list = new ArrayList<>();
      // Add elements
      ListIterator<String> listIterator = list.listIterator();
      return listIterator;
    } else {
      return Collections.emptyListIterator();
    }
  }

}

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