![How do I fix this error "
Exception in thread "main" java.lang.NullPointerException: Cannot invoke "String.hashCode()"
because "action" is null
at AddressBook.main(AddressBook.java:25)"
import java.util.Scanner;
public class AddressBook {
public static void main(String[] args) {
Tablea addressBook = new Tablea();
Scanner scanner = new Scanner(System.in);
String name, address;
String action = null;
boolean moreEntries = true;
while (moreEntries) {
System.out.println("/nMenu");
System.out.println("n.Add Entry");
System.out.println("d. Delete Entry");
System.out.println("u. Update Entry");
System.out.println("l. Search");
System.out.println("a. View All");
System.out.println("q. Exit");
// Insert a new entry into the address book
switch (action) {
case "n":
System.out.print("Enter a name: ");
name = scanner.nextLine();
System.out.print("Enter an address: ");
address = scanner.nextLine();
addressBook.insert(name, address);
System.out.println("New Contact has been added,");
System.out.print("Add another entry? (y/n): ");
String answer = scanner.nextLine().toLowerCase();
moreEntries = answer.equals("y") || answer.equals("yes");](https://image.slidesharecdn.com/howdoifixthiserror-exceptioninthread-main-java-lang-nullpoi-230316093129-e0fa8dcd/85/How-do-I-fix-this-error-Exception-in-thread-main-java-lang-NullPoi-pdf-1-320.jpg)
How do I fix this error - Exception in thread -main- java-lang-NullPoi.pdf
- 1. How do I fix this error " Exception in thread "main" java.lang.NullPointerException: Cannot invoke "String.hashCode()" because "action" is null at AddressBook.main(AddressBook.java:25)" import java.util.Scanner; public class AddressBook { public static void main(String[] args) { Tablea addressBook = new Tablea(); Scanner scanner = new Scanner(System.in); String name, address; String action = null; boolean moreEntries = true; while (moreEntries) { System.out.println("/nMenu"); System.out.println("n.Add Entry"); System.out.println("d. Delete Entry"); System.out.println("u. Update Entry"); System.out.println("l. Search"); System.out.println("a. View All"); System.out.println("q. Exit"); // Insert a new entry into the address book switch (action) { case "n": System.out.print("Enter a name: "); name = scanner.nextLine(); System.out.print("Enter an address: "); address = scanner.nextLine(); addressBook.insert(name, address); System.out.println("New Contact has been added,"); System.out.print("Add another entry? (y/n): "); String answer = scanner.nextLine().toLowerCase(); moreEntries = answer.equals("y") || answer.equals("yes");
- 2. break; // Delete an entry from the address book case "d": System.out.println("Enter a name to delete: "); name = scanner.nextLine(); boolean deleted = addressBook.delete(name); if (deleted) { System.out.println("Address deleted"); } else { System.out.println("Name not found"); } break; // Update an entry in the address book case "u": System.out.print("Enter a name to update: "); name = scanner.nextLine(); System.out.print("Enter a new address: "); address = scanner.nextLine(); boolean updated = addressBook.update(name, address); if (updated) { System.out.println("Address updated"); } else { System.out.println("Name not found"); } break; // Lookup an entry in the address book case "l": System.out.print("Enter a name to look up: "); name = scanner.nextLine(); String result = addressBook.lookUp(name); if (result != null) { System.out.println("Address: " + result); } else {
- 3. System.out.println("Name not found"); } break; // Display all entries in the address book case "a": System.out.println("All entries:"); addressBook.displayAll(); break; // Quit the program case"q": System.out.println("Quitting..."); } } } } Other files that go with it public class Node { private String name; private String address; private Node next; Node() { // add here .. } Node(String name, String address) { // add here .. this.name = name; this.address = address; this.next = null; } public String getKey() { // add here .. return this.name; }
- 4. public void setKey(String name) { // add here .. this.name = name; } public String getValue() { // add here .. return this.address; } public void setValue(String address) { // add here .. this.address = address; } public Node getNext() { // add here .. return this.next; } public void setNext(Node next) { // add here .. this.next = next; } } import java.util.Scanner; public class Tablea { private Node mark; public Node getMark() { return this.mark; } public void setMark(Node mark) { this.mark = mark; } public boolean insert(String name, String address) { Node newNode= new Node(name,address); if (this.mark== null) { this.mark = newNode; }else {
- 5. newNode.setNext(this.mark.getNext()); this.mark.setNext(newNode); } return true; } public String lookUp(String name) { Node current = this.mark; while(current!=null) { if (current.getKey().equals(name)) { return current.getValue(); } current = current.getNext(); } return null; } public boolean delete(String name) { Node current = this.mark; Node prev = null; while (current!= null) { if (current.getKey().equals(name)) { if (prev == null) { this.mark = current.getNext(); }else { prev.setNext(current.getNext()); } return true; } prev = current; current = current.getNext(); } return false; } public boolean update(String name, String newValue) { Node current = this.mark; while (current != null) { if (current.getKey().equals(name)) { current.setValue(newValue); return true; } current = current.getNext(); } return false; }
- 6. public boolean markToStart() { if (this.mark== null) { return false; } this.mark = null; return true; } public boolean advanceMark() { if (this.mark== null) { return false; } this.mark = this.mark.getNext(); return true; } public String keyAtMark() { if (this.mark== null) { return null; } return this.mark.getKey(); } public String valueAtMark() { if (this.mark== null) { return null; } return this.mark.getValue(); } public int displayAll() { Node current = this.mark; int count = 0; while (current != null) { System.out.println(current.getKey()+":"+ current); } return count; } }