Am relatively new to java so I have no idea what the problem is. In my getter settings of this class, I'm trying to evaluate if the input is of integer 1, 2 or 3, then it will return one of the previously saved setters described here. I used the same conditional statements in the setter, but the getter tells me that my method needs to return type int. What am I doing wrong? Or should I be doing this a completely different way? lol.
public class AssignmentMarks {
private String courseName;
private int assignment1 = 0, assignment2 = 0, assignment3 = 0;
public AssignmentMarks(String name, int mark1, int mark2, int mark3){
//create constructor to use variables.
this.courseName = name;
this.assignment1 = mark1;
this.assignment2 = mark2;
this.assignment3 = mark3;
}
public void setMark(int assignmentNumber, int mark) {
//assign value of the assignments
if(assignmentNumber == 1) {
mark = this.assignment1;
}else if(assignmentNumber == 2) {
mark = this.assignment2;
}else if(assignmentNumber == 3){
mark = this.assignment3;
}
}
public int getMark(int assignmentNum) {
if(assignmentNum == 1) {
return assignment1;
}else if (assignmentNum == 2) {
return assignment2;
} else if (assignmentNum == 3) {
return assignment3;
}
}
}
public int getMark(int assignmentNum) {
if(assignmentNum == 1) {
return assignment1;
}else if (assignmentNum == 2) {
return assignment2;
} else if (assignmentNum == 3) {
return assignment3;
}
// in another case
throw new Exception("Assignment must be 1, 2 or 3);
}
for setter
public void setMark(int assignmentNumber, int mark) {
//assign value of the assignments
if(assignmentNumber == 1) {
// BAD mark = this.assignment1; don't set parameter is useless
this.assignment1=mark;
}else if(assignmentNumber == 2) {
// BAD mark = this.assignment2;
this.assignment2=mark;
}else if(assignmentNumber == 3){
// BAD mark = this.assignment3;
this.assignment3=mark;
}
// in another case
throw new Exception("Assignment must be 1, 2 or 3");
}
I don't remember if you must import Exception for throwing them.
if yes put import java.lang.Exception on top of your code.
your logic can be improved using arrays, but let's walk, and after you will running...
Related
I need an advice for my code. What I want to do is insert a row into a table using Entity Framework Core in ASP.NET Core.
Before inserting new data, I want to check if email and phone number is already used or not.
I want to return specifically, example if return = x, email used. If return = y, phone used.
Here's my code
public int Insert(Employee employee)
{
var checkEmail = context.Employees.Single(e => e.Email == employee.Email);
if (checkEmail != null)
{
var checkPhone = context.Employees.Single(e => e.Phone == employee.Phone);
if (checkPhone != null)
{
context.Employees.Add(employee);
context.SaveChanges();
return 1;
}
return 2;
}
return 3;
}
I'm not sure with my code, is there any advice for the best practice in my case?
I just don't like these "magic numbers" that indicate the result of your checks.... how are you or how is anyone else going to know what 1 or 2 means, 6 months down the road from now??
I would suggest to either at least create a constants class that make it's more obvious what these numbers mean:
public class CheckConstants
{
public const int Successful = 1;
public const int PhoneExists = 2;
public const int EmailExists = 3;
}
and then use these constants in your code:
public int Insert(Employee employee)
{
var checkEmail = context.Employees.Single(e => e.Email == employee.Email);
if (checkEmail != null)
{
var checkPhone = context.Employees.Single(e => e.Phone == employee.Phone);
if (checkPhone != null)
{
context.Employees.Add(employee);
context.SaveChanges();
return CheckConstants.Successful;
}
return CheckConstants.PhoneExists;
}
return CheckConstants.EmailExists;
}
and also in any code that calls this method and need to know about the return status code.
Alternatively, you could also change this to an enum (instead of an int):
public enum CheckConstants
{
Successful, PhoneExists, EmailExists
}
and then just return this enum - instead of an int - from your method:
public CheckConstants Insert(Employee employee)
{
var checkEmail = context.Employees.Single(e => e.Email == employee.Email);
if (checkEmail != null)
{
var checkPhone = context.Employees.Single(e => e.Phone == employee.Phone);
if (checkPhone != null)
{
context.Employees.Add(employee);
context.SaveChanges();
return CheckConstants.Successful;
}
return CheckConstants.PhoneExists;
}
return CheckConstants.EmailExists;
}
merge two database check to one Query
use SingleOrDefault instance of Single
public int Insert(Employee employee)
{
var checkEmail = context.Employees.Select (e=>new {e.Email , e.Phone }).SingleOrDefault(e => e.Email == employee.Email || e.Phone == employee.Phone);
if (checkEmail == null)
{
context.Employees.Add(employee);
context.SaveChanges();
return 1;
}
else if (checkEmail.Email == employee.Email)
return 3;
else
return 2;
}
(The surface area of the ByteBuddy API is overwhelmingly enormous, which is why I'm asking the question.)
I'm aware that I can take a TypeDescription.Generic and determine its "sort" and proceed rather laboriously "by hand" from there, but often times I've found there is a method buried somewhere that will do this sort of tedious work for me.
EDIT: a commenter asked for the "tedious" recipe. Here it is (stand back; please note the various implementations of various Types are more or less what you'd expect them to be):
public static final Type toType(final TypeDefinition type) throws ReflectiveOperationException {
final Type returnValue;
if (type == null) {
returnValue = null;
} else {
final TypeDescription.Generic genericType = type.asGenericType();
switch (type.getSort()) {
case GENERIC_ARRAY:
returnValue = new DefaultGenericArrayType(toType(type.getComponentType()));
break;
case NON_GENERIC:
returnValue = Class.forName(type.getTypeName(), false, Thread.currentThread().getContextClassLoader());
break;
case PARAMETERIZED:
final TypeDefinition ownerType = genericType.getOwnerType();
final TypeDefinition rawType = type.asErasure();
final List<? extends TypeDefinition> actualTypeArguments = genericType.getTypeArguments();
if (actualTypeArguments == null || actualTypeArguments.isEmpty()) {
returnValue = new DefaultParameterizedType(toType(ownerType), toType(rawType));
} else {
final Type[] actualJavaTypeArguments = new Type[actualTypeArguments.size()];
for (int i = 0; i < actualTypeArguments.size(); i++) {
actualJavaTypeArguments[i] = toType(actualTypeArguments.get(i));
}
returnValue = new DefaultParameterizedType(toType(ownerType), toType(rawType), actualJavaTypeArguments);
}
break;
case VARIABLE:
final TypeVariableSource typeVariableSource = genericType.getTypeVariableSource();
final GenericDeclaration gd;
if (typeVariableSource instanceof TypeDefinition typeDefinition) {
gd = Class.forName(typeDefinition.asErasure().getTypeName(), false, Thread.currentThread().getContextClassLoader());
} else if (typeVariableSource instanceof MethodDescription.InDefinedShape methodDescription) {
// Reflection time
final String name = methodDescription.getName();
final Class<?> cls = Class.forName(methodDescription.getDeclaringType().asErasure().getTypeName(), false, Thread.currentThread().getContextClassLoader());
final List<? extends TypeDefinition> parameterTypes = methodDescription.getParameters().asTypeList();
final Class<?>[] parameterClasses = new Class<?>[parameterTypes.size()];
for (int i = 0; i < parameterTypes.size(); i++) {
parameterClasses[i] = Class.forName(parameterTypes.get(i).asErasure().getName(), false, Thread.currentThread().getContextClassLoader());
}
if (MethodDescription.CONSTRUCTOR_INTERNAL_NAME.equals(name)) {
assert TypeDescription.VOID.equals(methodDescription.getReturnType());
gd = cls.getDeclaredConstructor(parameterClasses);
} else {
assert !MethodDescription.TYPE_INITIALIZER_INTERNAL_NAME.equals(name);
gd = cls.getDeclaredMethod(name, parameterClasses);
}
} else {
throw new IllegalArgumentException("Unexpected type variable source: " + typeVariableSource);
}
final TypeVariable<?>[] typeVariables = gd.getTypeParameters();
TypeVariable<?> temp = null;
for (final TypeVariable<?> typeVariable : typeVariables) {
if (typeVariable.getName().equals(genericType.getSymbol())) {
temp = typeVariable;
break;
}
}
assert temp != null;
returnValue = temp;
break;
case VARIABLE_SYMBOLIC:
throw new IllegalArgumentException("Unexpected type: " + type);
case WILDCARD:
final List<? extends TypeDefinition> upperBounds = genericType.getUpperBounds();
final List<? extends TypeDefinition> lowerBounds = genericType.getLowerBounds();
if (lowerBounds == null || lowerBounds.isEmpty()) {
if (upperBounds == null || upperBounds.isEmpty() || (upperBounds.size() == 1 && TypeDescription.Generic.OBJECT.equals(upperBounds.get(0)))) {
returnValue = UnboundedWildcardType.INSTANCE;
} else {
// Upper bounded.
final Type[] upperJavaBounds = new Type[upperBounds.size()];
for (int i = 0; i < upperBounds.size(); i++) {
upperJavaBounds[i] = toType(upperBounds.get(i)); // XXX recursive
}
returnValue = new UpperBoundedWildcardType(upperJavaBounds);
}
} else {
assert upperBounds == null || upperBounds.isEmpty() || (upperBounds.size() == 1 && TypeDescription.Generic.OBJECT.equals(upperBounds.get(0))) : "Unexpected upper bounds: " + upperBounds + "; lower bounds: " + lowerBounds;
// Lower bounded.
assert lowerBounds.size() == 1 : "Unexpected size in lower bounds: " + lowerBounds;
returnValue = new LowerBoundedWildcardType(toType(lowerBounds.get(0))); // XXX recursive
}
break;
default:
throw new IllegalArgumentException("Unexpected type: " + type);
}
}
return returnValue;
}
No, you can only convert a Type to a TypeDescription.Generic but there is no option to do it the other way. The easiest option to emulate this would probably be to define a class that defines a field of the given Type, to load this class and to read the field type using Java reflection.
The reason Byte Buddy cannot convert a description to a Type is that Byte Buddy abstracts out class loaders and that type variables might be detached from their declaring source.
I am trying to get this loop to ask the question again what the user inputs not a 1 or a 2 but it puts me in a infinite loop how do i get out?
package vga;
import java.util.Scanner;
public class FPS_Info {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
boolean placeHolder;
String gameList[] = new String[2];
gameList[0] = ("Battlefield 1");
gameList[1] = ("Call Of Duty WWII");
System.out.printf("Please slect from theses games %s or %s.%nType 1 for %s and type 2 for %s.%n",
gameList[0], gameList[1], gameList[0], gameList[1]);
int gameSelection = scanner.nextInt();
if (gameSelection == 1 || gameSelection ==2) {
placeHolder = true;
}
while (placeHolder = true) {
if (gameSelection == 1) {
System.out.println("Battlefield 1, good choice.");
break;
} else if (gameSelection == 2) {
System.out.println("Call Of Duty WWII, good selection.");
break;
} else {
System.out.println("Please enter one of the options.");
placeHolder = false;
}
}
}
}
If you restructure your code, you don't need the placeholder.
import java.util.Scanner;
public class FPS_Info {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
boolean placeHolder;
String gameList[] = new String[2];
gameList[0] = ("Battlefield 1");
gameList[1] = ("Call Of Duty WWII");
System.out.printf("Please slect from theses games %s or %s.%nType 1 for %s and type 2 for %s.%n",
gameList[0], gameList[1], gameList[0], gameList[1]);
int gameSelection = scanner.nextInt();
while (gameSelection != 1 && gameSelection != 2) { // or while (gameSelection > 0 && gameSelection <= gameList.length)
System.out.println("Please enter one of the options.");
gameSelection = scanner.nextInt();
}
if (gameSelection == 1) {
System.out.println("Battlefield 1, good choice.");
}
else if (gameSelection == 2) {
System.out.println("Call Of Duty WWII, good selection.");
}
}
}
Your code includes:
while (placeHolder = true)
You probably meant placeHolder == true. The = assigns true rather than checks against it, so it's not doing the loop like you probably meant.
That said, there's no reason to == true in the first place. You can just
while (placeHolder)
package LinkList2;
//import java.util.*;
public class Duplicates {
public static void removeDuplicates(LinkedListNode head)
{
LinkedListNode current = head;
while(current!= null && current.next!= null)
{
LinkedListNode curr = current;
while(curr!=null)
{
if(curr.next.data==current.data) //Getting error at this line
curr.next = curr.next.next;
else
curr = curr.next;
}
current = current.next;
}
}
public static void main(String args[])
{
LinkedListNode first = new LinkedListNode(0,null,null);
LinkedListNode head = first;
LinkedListNode second = first;
for(int i=1; i< 8; i++)
{
second = new LinkedListNode(i%2, null, null);
first.setNext(second);
second.setPrevious(first);
}
System.out.println(head.printForward());
removeDuplicates(head);// Getting error at this line
}
}
Getting null pointer exception in the above code. When I try to run the above code, it gives null pointer exception.
Please help me with my mistake.
Below is the implementation of LinkList where all the methods are defined
class LinkedListNode {
public LinkedListNode next;
public LinkedListNode prev;
public LinkedListNode last;
public int data;
public LinkedListNode(int d, LinkedListNode n, LinkedListNode p) {
data = d;
setNext(n);
setPrevious(p);
}
public void setNext(LinkedListNode n) {
next = n;
if (this == last) {
last = n;
}
if (n != null && n.prev != this) {
n.setPrevious(this);
}
}
public void setPrevious(LinkedListNode p) {
prev = p;
if (p != null && p.next != this) {
p.setNext(this);
}
}
public String printForward() {
if (next != null) {
return data + "->" + next.printForward();
} else {
return ((Integer) data).toString();
}
}
public LinkedListNode clone() {
LinkedListNode next2 = null;
if (next != null) {
next2 = next.clone();
}
LinkedListNode head2 = new LinkedListNode(data, next2, null);
return head2;
}
}
You are getting an exception just because of the following condition:
while(curr != null)
Replace it with while(curr != null && curr.next != null) this way you can check if you have the next element.
Hope this helps.
The problem is that here:
while(curr != null)
{
if(curr.next.data==current.data) //Getting error at this line
curr.next = curr.next.next;
else
curr = curr.next;
}
You are accessing the curr.next.data where you are not checking if that node is null or not. This through your NullPointerException.
To fix your problem is to check on the while loop, if the .next is also not null.
while(curr != null && curr.next != null)
{
if(curr.next.data==current.data) //Getting error at this line
curr.next = curr.next.next;
else
curr = curr.next;
}
In other words, you are not checking if your next node is actually the end of the linked list (i.e null). If you need in your program logic to handle this separately, then you should remove the check from the while loop, and implement this check differently.
I am trying to follow Trees tutorial at: http://cslibrary.stanford.edu/110/BinaryTrees.html
Here is the code I have written so far:
package trees.bst;
import java.util.ArrayList;
import java.util.List;
import java.util.StringTokenizer;
/**
*
* #author sachin
*/
public class BinarySearchTree {
Node root = null;
class Node {
Node left = null;
Node right = null;
int data = 0;
public Node(int data) {
this.left = null;
this.right = null;
this.data = data;
}
}
public void insert(int data) {
root = insert(data, root);
}
public boolean lookup(int data) {
return lookup(data, root);
}
public void buildTree(int numNodes) {
for (int i = 0; i < numNodes; i++) {
int num = (int) (Math.random() * 10);
System.out.println("Inserting number:" + num);
insert(num);
}
}
public int size() {
return size(root);
}
public int maxDepth() {
return maxDepth(root);
}
public int minValue() {
return minValue(root);
}
public int maxValue() {
return maxValue(root);
}
public void printTree() { //inorder traversal
System.out.println("inorder traversal:");
printTree(root);
System.out.println("\n--------------");
}
public void printPostorder() { //inorder traversal
System.out.println("printPostorder traversal:");
printPostorder(root);
System.out.println("\n--------------");
}
public int buildTreeFromOutputString(String op) {
root = null;
int i = 0;
StringTokenizer st = new StringTokenizer(op);
while (st.hasMoreTokens()) {
String stNum = st.nextToken();
int num = Integer.parseInt(stNum);
System.out.println("buildTreeFromOutputString: Inserting number:" + num);
insert(num);
i++;
}
return i;
}
public boolean hasPathSum(int pathsum) {
return hasPathSum(pathsum, root);
}
public void mirror() {
mirror(root);
}
public void doubleTree() {
doubleTree(root);
}
public boolean sameTree(BinarySearchTree bst) { //is this tree same as another given tree?
return sameTree(this.root, bst.getRoot());
}
public void printPaths() {
if (root == null) {
System.out.println("print path sum: tree is empty");
}
List pathSoFar = new ArrayList();
printPaths(root, pathSoFar);
}
///-------------------------------------------Public helper functions
public Node getRoot() {
return root;
}
//Exporting a non public Type through public API
///-------------------------------------------Helper Functions
private boolean isLeaf(Node node) {
if (node == null) {
return false;
}
if (node.left == null && node.right == null) {
return true;
}
return false;
}
///-----------------------------------------------------------
private boolean sameTree(Node n1, Node n2) {
if ((n1 == null && n2 == null)) {
return true;
} else {
if ((n1 == null || n2 == null)) {
return false;
} else {
if ((n1.data == n2.data)) {
return (sameTree(n1.left, n2.left) && sameTree(n1.right, n2.right));
}
}
}
return false;
}
private void doubleTree(Node node) {
//create a copy
//bypass the copy to continue looping
if (node == null) {
return;
}
Node copyNode = new Node(node.data);
Node temp = node.left;
node.left = copyNode;
copyNode.left = temp;
doubleTree(copyNode.left);
doubleTree(node.right);
}
private void mirror(Node node) {
if (node == null) {
return;
}
Node temp = node.left;
node.left = node.right;
node.right = temp;
mirror(node.left);
mirror(node.right);
}
private void printPaths(Node node, List pathSoFar) {
if (node == null) {
return;
}
pathSoFar.add(node.data);
if (isLeaf(node)) {
System.out.println("path in tree:" + pathSoFar);
pathSoFar.remove(pathSoFar.lastIndexOf(node.data)); //only the current node, a node.data may be duplicated
return;
} else {
printPaths(node.left, pathSoFar);
printPaths(node.right, pathSoFar);
}
}
private boolean hasPathSum(int pathsum, Node node) {
if (node == null) {
return false;
}
int val = pathsum - node.data;
boolean ret = false;
if (val == 0 && isLeaf(node)) {
ret = true;
} else if (val == 0 && !isLeaf(node)) {
ret = false;
} else if (val != 0 && isLeaf(node)) {
ret = false;
} else if (val != 0 && !isLeaf(node)) {
//recurse further
ret = hasPathSum(val, node.left) || hasPathSum(val, node.right);
}
return ret;
}
private void printPostorder(Node node) { //inorder traversal
if (node == null) {
return;
}
printPostorder(node.left);
printPostorder(node.right);
System.out.print(" " + node.data);
}
private void printTree(Node node) { //inorder traversal
if (node == null) {
return;
}
printTree(node.left);
System.out.print(" " + node.data);
printTree(node.right);
}
private int minValue(Node node) {
if (node == null) {
//error case: this is not supported
return -1;
}
if (node.left == null) {
return node.data;
} else {
return minValue(node.left);
}
}
private int maxValue(Node node) {
if (node == null) {
//error case: this is not supported
return -1;
}
if (node.right == null) {
return node.data;
} else {
return maxValue(node.right);
}
}
private int maxDepth(Node node) {
if (node == null || (node.left == null && node.right == null)) {
return 0;
}
int ldepth = 1 + maxDepth(node.left);
int rdepth = 1 + maxDepth(node.right);
if (ldepth > rdepth) {
return ldepth;
} else {
return rdepth;
}
}
private int size(Node node) {
if (node == null) {
return 0;
}
return 1 + size(node.left) + size(node.right);
}
private Node insert(int data, Node node) {
if (node == null) {
node = new Node(data);
} else if (data <= node.data) {
node.left = insert(data, node.left);
} else {
node.right = insert(data, node.right);
}
//control should never reach here;
return node;
}
private boolean lookup(int data, Node node) {
if (node == null) {
return false;
}
if (node.data == data) {
return true;
}
if (data < node.data) {
return lookup(data, node.left);
} else {
return lookup(data, node.right);
}
}
public static void main(String[] args) {
BinarySearchTree bst = new BinarySearchTree();
int treesize = 5;
bst.buildTree(treesize);
//treesize = bst.buildTreeFromOutputString("4 4 4 6 7");
treesize = bst.buildTreeFromOutputString("3 4 6 3 6");
//treesize = bst.buildTreeFromOutputString("10");
for (int i = 0; i < treesize; i++) {
System.out.println("Searching:" + i + " found:" + bst.lookup(i));
}
System.out.println("tree size:" + bst.size());
System.out.println("maxDepth :" + bst.maxDepth());
System.out.println("minvalue :" + bst.minValue());
System.out.println("maxvalue :" + bst.maxValue());
bst.printTree();
bst.printPostorder();
int pathSum = 10;
System.out.println("hasPathSum " + pathSum + ":" + bst.hasPathSum(pathSum));
pathSum = 6;
System.out.println("hasPathSum " + pathSum + ":" + bst.hasPathSum(pathSum));
pathSum = 19;
System.out.println("hasPathSum " + pathSum + ":" + bst.hasPathSum(pathSum));
bst.printPaths();
bst.printTree();
//bst.mirror();
System.out.println("Tree after mirror function:");
bst.printTree();
//bst.doubleTree();
System.out.println("Tree after double function:");
bst.printTree();
System.out.println("tree size:" + bst.size());
System.out.println("Same tree:" + bst.sameTree(bst));
BinarySearchTree bst2 = new BinarySearchTree();
bst2.buildTree(treesize);
treesize = bst2.buildTreeFromOutputString("3 4 6 3 6");
bst2.printTree();
System.out.println("Same tree:" + bst.sameTree(bst2));
System.out.println("---");
}
}
Now the problem is that netbeans shows Warning: Exporting a non public Type through public API for function getRoot().
I write this function to get root of tree to be used in sameTree() function, to help comparison of "this" with given tree.
Perhaps this is a OOP design issue... How should I restructure the above code that I do not get this warning and what is the concept I am missing here?
The issue here is that some code might call getRoot() but won't be able to use it's return value since you only gave package access to the Node class.
Make Node a top level class with its own file, or at least make it public
I don't really understand why you even created the getRoot() method. As long as you are inside your class you can even access private fields from any other object of the same class.
So you can change
public boolean sameTree(BinarySearchTree bst) { //is this tree same as another given tree?
return sameTree(this.root, bst.getRoot());
}
to
public boolean sameTree(BinarySearchTree bst) { //is this tree same as another given tree?
return sameTree(this.root, bst.root);
}
I would also add a "short path" for the case you pass the same instance to this method:
public boolean sameTree(BinarySearchTree bst) { //is this tree same as another given tree?
if (this == bst) {
return true;
}
return sameTree(this.root, bst.root);
}