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Access other Java classes

I am a Java beginner and two questions boggle me really hard, so I have these questions.
For instance, I do not understand why in the Class Suitcase the method call getWeight() can be called, but in the Class Hold the method call totalWeight() not.
It works here:
public int totalWeight() {
int momentaryWeight = 0;
for (Item items: this.itemList) {
momentaryWeight = momentaryWeight + items.getWeight();
}
return momentaryWeight;
}
But not here:
public String toString() {
int momentaryWeight = 0;
int index = 0;
for (int i = index; i < this.suitcaseList.size(); i++) {
Suitcase suitcaseChosen = this.suitcaseList.get(i);
int weightOfsuitcaseChosen = suitcaseChosen.totalWeight();
momentaryWeight += weightOfsuitcaseChosen;
}
Also when having a method that returns something and using an if statement (so 2 return statements) it asks me afterwards for another return statement, like here:
public Item printGoods() {
if (this.itemList.isEmpty() == true) {
return null;
} else {
for (Item itemThis: this.itemList) {
return itemThis;
}
}
return null;
}
I know that maybe these are dull questions, but I couldn't think of a better forum to understand it.
Thanks.
The Hold class:
public class Hold {
private int maxWeight;
private ArrayList<Suitcase> suitcaseList;
public Hold(int maxWeightGiven) {
this.maxWeight = maxWeightGiven;
this.suitcaseList = new ArrayList<>();
}
public void addSuitcase(Suitcase suitcase) {
this.suitcaseList.add(suitcase);
}
public String toString() {
int momentaryWeight = 0;
int index = 0;
for (int i = index; i < this.suitcaseList.size(); i++) {
Suitcase suitcaseChosen = this.suitcaseList.get(i);
int weightOfsuitcaseChosen = suitcaseChosen.totalWeight();
momentaryWeight += weightOfsuitcaseChosen;
}
return this.suitcaseList.size() + " suitcases" + " (" + momentaryWeight + " kg)";
}
The Suitcase class:
import java.util.ArrayList;
public class Suitcase {
private int maximumWeight;
private ArrayList<Item> itemList;
public Suitcase(int maximumWeightGiven) {
this.maximumWeight = maximumWeightGiven;
this.itemList = new ArrayList<>();
}
public void addItem(Item item) {
int momentaryWeight = 0;
if (momentaryWeight <= this.maximumWeight && momentaryWeight + item.getWeight() <= this.maximumWeight) {
this.itemList.add(item);
}
}
public int totalWeight() {
int momentaryWeight = 0;
for (Item items: this.itemList) {
momentaryWeight = momentaryWeight + items.getWeight();
}
return momentaryWeight;
}
The class Item looks like this:
public class Item {
private String name;
private int weight;
public Item(String nameGiven, int weightGiven) {
this.name = nameGiven;
this.weight = weightGiven;
}
public String getName() {
return this.name;
}
public int getWeight() {
return this.weight;
}
public String toString() {
return this.name + "( " + this.weight + " kg)";
}
}
}

First question is incomplete code and detail.
Second question: suppose if-condition is false and your loop condition is also false(empty array) then the program will not reach to return statement that's why you have to add an extra return statement.
You can move last return line inside the else block

Don't know what happened, but as I worked on it a while later, suddenly the error messages disappeared and I was able to run the program. Is there a special key in NetBeans for "Refreshing"?

How to Implement Binary Search Manually In My Own ADT [ JAVA ]

Alright I am stuck on how do I implement this binary search that will receive data from other classes.
I am trying to implement it in my own ADT.
I have implemented a List ADT manually but now I want to add in a search operation which utilizes binary search algorithm manually and doesn't uses any built in Java API.
Example this is my sorted list interface that I implemented manually.
public class SortedArrayList<T extends Comparable<T>> implements SortedListInterface<T>{
private boolean binarySearch(// What parameters should I receive from Student Object?) {
// This will be my binary search implementation
}
}
The problem is I will be creating a Student class where I will add the instances of the student class into the sortedArrayList above.
Like how am I going to receive the data to be put into the binary search algorithm in a generics typed sortedArrayList?
Do note I am not allowed to use any JAVA Built-IN API , everything must be implemented manually else I can finish this easily but its a pain now since its limited.
Example I want to binary search by Student name from Student's class. How will I need to implement and receive data into this manually implemented ADT of mine?
public class SortedArrayList<T extends Comparable<T>> implements SortedListInterface<T>{
private T[] list;
private boolean binarySearch(int first, int last, T desiredItem) {
int mid = (first + last) / 2;
if(desiredItem.getFullName().equals(list[mid])
// This part over here. How do I access attributes from Student class in this ADT so that I can access the data and do comparison for the binary search..
}
}
How do I access attributes from Student class into my own ADT so that I can do comparisons on binary search algorithm?!
I am literally stuck.
I would appreciate someone giving me directions.
I repeat again no BUILT-IN APIs from JAVA, implementation manually only
ADT SortedList Interface
public interface SortedListInterface <T extends Comparable<T>> {
public boolean add(T element);
public T get(int index);
public boolean search(T element);
public T remove(int index);
public void clear();
public int getLength();
public boolean isEmpty();
public boolean isFull();
}
ADT SortedList Implementation Code
public class SortedArrayList<T extends Comparable<T>> implements SortedListInterface<T>{
//Data Types
private T[] list;
private int length;
private static final int SIZE = 10;
// Constructors
public SortedArrayList() {
this(SIZE);
}
public SortedArrayList(int size) {
length = 0;
list = (T[]) new Comparable[SIZE]; // an array of instances of a class implementing Comparable interface and able to use compareto method but its overidden instead
}
// Setter & Getters
#Override
public int getLength() {
return length;
}
#Override
public boolean isEmpty() {
return length == 0;
}
#Override
public boolean isFull() {
return false;
}
#Override
public void clear() {
length = 0;
}
// Array Expansion
private boolean isArrayFull() {
return length == list.length;
}
private void expandArray() {
T[] oldList = list;
int oldSize = oldList.length;
list = (T[]) new Object[2 * oldSize];
for (int i = 0; i < oldSize; i++) // copy old array elements into new array elements
list[i] = oldList[i];
}
// ADT METHODs
// Add New Elements Function
#Override
public boolean add(T element) {
int i = 0;
while (i < length && element.compareTo(list[i]) > 0) // return 0 with equal , return more than 1 if element larger than list[i] , return -1 if less
i++;
makeRoom(i + 1);
list[i] = element;
length++;
return true;
}
private void makeRoom(int index) { // accepts given index
int newIndex = index - 1;
int lastIndex = length - 1;
for (int i = lastIndex; i >= newIndex; i--)
list[i + 1] = list[i];
}
//Remove Elements Function
#Override
public T remove(int index) { // accepts given index
T result = null;
if ( index >= 1 && index <= length ) {
result = list[index - 1];
if (index < length)
removeGap(index);
length--;
}
return result;
}
private void removeGap(int index) { // accepts given index and remove the gap where the element its removed
int removedIndex = index - 1;
int lastIndex = length - 1;
for (int i = removedIndex; i < lastIndex; i++)
list[i] = list[i + 1]; // shifts elements back to remove the gap
}
// Get Element
#Override
public T get(int index) { // accepts given index and return the object
T object = null;
if ( index >= 1 && index <= length)
object = list[index - 1];
return object;
}
// Search Algorithms
#Override
public boolean search(T element) {
return binarySearch(element);
}
private boolean binarySearch(// Implementation here) {
// Implementation here
}
//To String Method
#Override
public String toString() {
String result = "";
for (int i = 0; i < length; i++)
result += list[i] + "\n";
return result;
}
}
Student Class Implementation
public class Student implements Comparable<Student>{
// Data Types
private Name name;
private char gender;
private String icNo;
private String mobileNo;
private Course course;
private int group;
private String dOB;
// Constructors
public Student() {
}
public Student(Name name, char gender, String icNo, String mobileNo, Course course, int group, String dOB) {
this.name = name;
this.gender = gender;
this.icNo = icNo;
this.mobileNo = mobileNo;
this.course = course;
this.group = group;
this.dOB = dOB;
}
public Student(Name name) {
this.name = name;
}
// setter
public void setName(Name name) {
this.name = name;
}
public void setGender(char gender) {
this.gender = gender;
}
public void setIcNo(String icNo) {
this.icNo = icNo;
}
public void setMobileNo(String mobileNo) {
this.mobileNo = mobileNo;
}
public void setCourse(Course course) {
this.course = course;
}
public void setGroup(int group) {
this.group = group;
}
public void setdOB(String dOB) {
this.dOB = dOB;
}
// getter
public Name getName() {
return name;
}
public char getGender() {
return gender;
}
public String getIcNo() {
return icNo;
}
public String getMobileNo() {
return mobileNo;
}
public Course getCourse() {
return course;
}
public int getGroup() {
return group;
}
public String getdOB() {
return dOB;
}
#Override
public String toString() {
return "Student{" + "name=" + name + ", gender=" + gender + ", icNo=" + icNo + ", mobileNo=" + mobileNo + ", course=" + course + ", group=" + group + ", dOB=" + dOB + '}';
}
public int compareTo(Student object) { // Sort according to name if name same then sort according to gender and so on.
int c = this.name.getFullName().compareTo(object.getName().getFullName());
if(c == 0)
c = this.gender - object.getGender();
if(c == 0)
c = this.icNo.compareTo(object.getIcNo());
if(c == 0)
c = this.mobileNo.compareTo(object.getMobileNo());
if(c == 0)
c = this.group - object.getGroup();
if(c == 0)
c = this.dOB.compareTo(object.getdOB());
return c;
}
}
Course Class
public class Course {
// Data Types
private String courseCode;
private String courseName;
private double courseFee;
// Constructors
public Course() {
}
public Course(String courseCode, String courseName, double courseFee) {
this.courseCode = courseCode;
this.courseName = courseName;
this.courseFee = courseFee;
}
// setter
public void setCourseCode(String courseCode) {
this.courseCode = courseCode;
}
public void setCourseName(String courseName) {
this.courseName = courseName;
}
public void setCourseFee(double courseFee) {
this.courseFee = courseFee;
}
// getter
public String getCourseCode() {
return courseCode;
}
public String getCourseName() {
return courseName;
}
public double getCourseFee() {
return courseFee;
}
#Override
public String toString() {
return "CourseCode = " + courseCode + "Course Name = " + courseName + "Course Fee = " + courseFee;
}
}
Name Class
public class Name {
// Data Types
private String firstName;
private String lastName;
// Constructors
public Name() {
}
public Name(String firstName, String lastName) {
this.firstName = firstName;
this.lastName = lastName;
}
// setter
public void setFirstName(String firstName) {
this.firstName = firstName;
}
public void setLastName(String lastName) {
this.lastName = lastName;
}
// getter
public String getFirstName() {
return firstName;
}
public String getLastName() {
return lastName;
}
public String getFullName(){
return firstName + " " + lastName;
}
#Override
public String toString() {
return "Name{" + "firstName=" + firstName + ", lastName=" + lastName + '}';
}

The binary search algorithm relies on comparing a value being searched for with values in the list being searched. That's why the declaration of your class that implements the SortedListInterface is:
SortedArrayList<T extends Comparable<T>>
Note the extends Comparable<T>.
Comparable is an interface through which you can compare two objects. Hence in the search() method that you have to implement, you know that every object in the list defines the compareTo() method and you simply use that method to compare the object being searched for with individual objects in the list.
Here is a simple implementation of the binary search algorithm in the context of your project.
private T[] list; // The list to search.
private int count; // The number of non-null elements in 'list'.
public boolean search(T element) {
boolean found = false;
int lo = 0;
int hi = count - 1;
while (lo <= hi) {
int mid = (lo + hi) / 2;
if (list[mid].compareTo(element) < 0) {
lo = mid + 1;
}
else if (list[mid].compareTo(element) > 0) {
hi = mid - 1;
}
else {
found = true;
break;
}
}
return found;
}
With a method, you have a method parameter. In the method code you use the parameter name. But when you invoke that method from other code, you provide a value which is substituted for the parameter. In the same way, the code above uses a type parameter which is substituted with the name of an actual class when you create an instance of class SortedArrayList. In your case, T is substituted with Student and class Student must implement the compareTo() method. Hence method search(), in class SortedArrayList does not need to know about the members in class Student.
So you would first create an instance of SortedArrayList like this:
SortedArrayList<Student> theList = new SortedArrayList<>();
Then you can call the search() method like this:
Student s = new Student(/* relevant parameter values */);
theList.search(s);
EDIT
I understand that you don't necessarily want to search for a Student, you may want to search for the Name of a student or a student's mobile phone number. In that case I believe you need a Comparator. Here is the code for class SortedArrayList with the addition of a Comparator
import java.util.Comparator;
import java.util.Objects;
public class SortedArrayList<T extends Comparable<T>> implements SortedListInterface<T> {
private static final int SIZE = 10;
private Comparator<? super T> comparator;
private T[] list;
private int count;
#SuppressWarnings("unchecked")
public SortedArrayList(Comparator<? super T> c) {
comparator = c;
list = (T[]) new Comparable[SIZE]; // No way to verify that 'list' only contains instances of 'T'.
/* NOTE: Following is not allowed.
list = new T[SIZE]; // Cannot create a generic array of T
*/
}
#Override
public boolean add(T element) {
Objects.requireNonNull(element, "Cannot add null element.");
boolean result = false;
if (count == 0) {
list[0] = element;
count = 1;
result = true;
}
else {
if (!isFull()) {
int i = 0;
while (list[i] != null) {
if (element.compareTo(list[i]) < 0) {
break;
}
i++;
}
if (list[i] != null) {
for (int j = count - 1; j >= i; j--) {
list[j + 1] = list[j];
}
}
list[i] = element;
count++;
result = true;
}
}
return result;
}
#Override
public T get(int index) {
checkIndex(index);
return list[index];
}
#Override
public boolean search(T element) {
if (comparator == null) {
return binarySearchComparable(element);
}
else {
return binarySearchComparator(element);
}
}
#Override
public T remove(int index) {
checkIndex(index);
T removed = list[index];
list[index] = null;
for (int i = index; i < count; i++) {
list[i] = list[i + 1];
}
count--;
list[count] = null;
return removed;
}
#Override
public void clear() {
for (int i = 0; i < count; i++) {
list[i] = null;
}
count = 0;
}
#Override
public int getLength() {
return count;
}
#Override
public boolean isEmpty() {
return count == 0;
}
#Override
public boolean isFull() {
return count == SIZE;
}
private boolean binarySearchComparable(T element) {
boolean found = false;
int lo = 0;
int hi = count - 1;
while (lo <= hi) {
int mid = (lo + hi) / 2;
if (list[mid].compareTo(element) < 0) {
lo = mid + 1;
}
else if (list[mid].compareTo(element) > 0) {
hi = mid - 1;
}
else {
found = true;
break;
}
}
return found;
}
private boolean binarySearchComparator(T key) {
int low = 0;
int high = count - 1;
while (low <= high) {
int mid = (low + high) >>> 1;
T midVal = list[mid];
int cmp = comparator.compare(midVal, key);
if (cmp < 0)
low = mid + 1;
else if (cmp > 0)
high = mid - 1;
else
return true; // key found
}
return false; // key not found.
}
private void checkIndex(int index) {
if (index < 0) {
throw new IllegalArgumentException("Negative index.");
}
if (index >= count) {
throw new IllegalArgumentException(String.format("Supplied index %d is not less than %d", index, count));
}
}
}
Here is an example Comparator for the Name of a Student
import java.util.Comparator;
public class NameComparator implements Comparator<Student> {
#Override
public int compare(Student student1, Student student2) {
int result;
if (student1 == null) {
if (student2 == null) {
result = 0;
}
else {
result = -1;
}
}
else {
if (student2 == null) {
result = 1;
}
else {
result = student1.getName().getFullName().compareTo(student2.getName().getFullName());
}
}
return result;
}
}
So in order to search the list according to any combination of Student attributes, simply implement an appropriate Comparator and pass it to the SortedArrayList class.
EDIT 2
Following your comments from November 17, 2019.
Below is code for a "name and mobile" Comparator. As I wrote in my previous Edit, you need to write an appropriate Comparator for a given combination of Student attributes.
import java.util.Comparator;
/**
* Compares {#code Student} name and mobile phone number.
*/
public class NameAndMobileComparator implements Comparator<Student> {
#Override
public int compare(Student student1, Student student2) {
int result;
if (student1 == null) {
if (student2 == null) {
result = 0;
}
else {
result = -1;
}
}
else {
if (student2 == null) {
result = 1;
}
else {
result = student1.getName().getFullName().compareTo(student2.getName().getFullName());
if (result == 0) {
result = student1.getMobileNo().compareTo(student2.getMobileNo());
}
}
}
return result;
}
}

Have a Queue with Generics implementation print specific Object attributes

I have created a simple Queue of type which is also contains a print() function to it.
public class ArrayQueue implements Queue {
private T[] theArray;
private int currentSize;
private int front;
private int back;
private static final int DEFAULT_CAPACITY = 10;
public ArrayQueue() {
theArray = (T[]) new Object[DEFAULT_CAPACITY];
currentSize = 0;
front = 0;
back = -1;
}
public boolean isEmpty() {
return currentSize == 0;
}
public T dequeue() throws EmptyQueueException {
if (isEmpty())
throw new EmptyQueueException("ArrayQueue dequeue error");
T returnValue = theArray[front];
front = increment(front);
currentSize--;
return returnValue;
}
public void enqueue(T x) {
if (currentSize == theArray.length)
doubleQueue();
back = increment(back);
theArray[back] = x;
currentSize++;
}
private int increment(int x) {
if (++x == theArray.length)
x = 0;
return x;
}
public void print() {
if (isEmpty()) {
System.out.printf("Empty queue\n");
return;
}
System.out.printf("The queue is: ");
for (int i = front; i != back; i = increment(i)) {
System.out.print(theArray[i] + " ");
}
System.out.print(theArray[back] + "\n");
}
I have also created a Song object with 3 variables
public class Song {
private int id;
private String name;
private int likes;
public Song() {
this(1,"Test",10);
}
public Song(int id,String name, int likes) {
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getLikes() {
return likes;
}
public void setLikes(int likes) {
this.likes = likes;
}
Is there a way modify this function in order to print a specific object's information or do i need to write a different print method during my implementation?
For example i would like my Print method to show all the objects variables , if i call just like this is will only get the object pointer
ArrayQueue<Song> arrayQueue = new ArrayQueue<Song>();
Queue<Song> queue = arrayQueue; //arrayQueue instance is also a Queue
Song s = new Song();
arrayQueue.enqueue(s);
arrayQueue.print();
Result is
The queue is: Song#15db9742
My modification would print :
The queue is : 1 Test 10

You need to override the toString() method of Song.
For example, add this to Song:
#Override
public String toString() {
return id + " " + name + " " + likes;
}

Java Generic treeMap with comparator declaration without warning

There is any way i can do next with out getting the yellow warning / #SuppressWarnings("unchecked")
Generics objects :
P=product to compare,C = custoumer
public static myComparator<Product<P>> comparator= new myComparator<Product<P>>();
comparator declaration is outside "insertIntoMap" method,
i cant use the Product object inside "insertIntoMap" method .
public static <P,C> TreeMap<P, C> insertIntoMap(LinkedHashSet<P> set,C[] ac){
#SuppressWarnings("unchecked")
TreeMap<P,C> treeMap = new TreeMap<P,C>((Comparator<? super P>) comparator);
int itrIndex=0;
Iterator<P> itr = set.iterator();
while(itr.hasNext()){
treeMap.put(itr.next(), ac[itrIndex]);
itrIndex++;
}
return (TreeMap<P, C>) treeMap;
}
public static class myComparator<E> implements Comparator<Product<? super E>>{
#Override
public int compare(Product<? super E> o1, Product<? super E> o2) {
if(o1.getName().length()>o2.getName().length())
return 1;
else return -1;
}
}
Product Class :
public static class Product<E> implements Comparable<E>{
private E serialNum;
private String name;
Product(E serialNum,String name){
setSerialNum(serialNum);
setName(name);
}
#Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result;
result = prime * result + ((serialNum == null) ? 0 : serialNum.hashCode());
return result;
}
#Override
public boolean equals(Object obj) {
Product<?> other = (Product<?>) obj;
if (serialNum.equals(other.serialNum))return true;
else return false;
}
public E getSerialNum() {
return serialNum;
}
public void setSerialNum(E serialNum) {
this.serialNum = serialNum;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String toString() {
return serialNum.toString()+": "+name;
}
#Override
public int compareTo(E o) {
if(this.hashCode()>o.hashCode())return 1;
else if(this.hashCode()<o.hashCode()) return -1;
else return -1;
}
}
Thanks !

From the code you posted it seems:
myComparator should not be generic:
public class myComperator implements Comparator<Product<?>> {
#Override
public int compare(Product<?> o1, Product<?> o2) {
if (o1.getName().length() > o2.getName().length())
return 1;
else if (o1.getName().length() < o2.getName().length())
return -1;
else
return -1;
}
}
insertIntoMap should only work for P extending Product. Otherwise you cannot use myComperator (which compares Products):
public static <P extends Product<?>, C> TreeMap<P, C> insertIntoMap(
LinkedHashSet<P> set, C[] ac) {
TreeMap<P, C> treeMap = new TreeMap<P, C>(new myComperator());
int itrIndex = 0;
Iterator<P> itr = set.iterator();
while (itr.hasNext()) {
treeMap.put(itr.next(), ac[itrIndex]);
itrIndex++;
}
return treeMap;
}

Can only iterate over an array

enum Bags {
SMALL(10832, 10000000), MEDIUM(10833, 100000000), HUGE(10834, 100000000), HEFTY(
10835, 2147000000);
public int id, mAmount;
Bags(int id, int mAmount) {
this.id = id;
this.mAmount = mAmount;
}
public int getId() {
return id;
}
public int getMoneyAmount() {
return mAmount;
}
public Bags getBagConfig(int index) {
for (Bags bag : Bags.values()) {
for (int bagId : bag.getId()) {
if (bagId == index) {
return bag;
}
}
}
return null;
}
}
public static void init(final Client c, final int itemUsed,
final int useWith) {
if (itemUsed == 7 && useWith == 1) {
c.getItems().deleteItem(7, 1);
}
c.eventContainer.addEvent(new CycleEvent(5) {
public void execute() {
c.getItems().addItem(1, 3);
}
});
}
It says: Can only iterate over an array or an instance of java.lang.Iterable
Can someone please help me out with this?
I don't know how to fix this error, the error is on the for loop.

The error message is correct, this
for (Bags bag : Bags.values()) {
for (int bagId : bag.getId()) { // <-- HERE!
if (bagId == index) {
return bag;
}
}
}
Is not legal. I think you wanted
for (Bags bag : Bags.values()) {
if (bag.getId() == index) {
return bag;
}
}
Because getId() returns a single int.

Replace this code:
for (int bagId : bag.getId()) {
if (bagId == index) {
return bag;
}
}
with
if (bag.getId() == index) {
return bag;
}