Multi-dimension Array Declaration And Instantiation?
May 17, 2015
Whilst pre-preparing for java certification, one of the online mock exams has slightly confused me by saying my answer was incorrect for multi-dimension array 'declaration and instantiation'.
This is one of the answers i chose - which was marked as incorrect
a)
int[][] array2d = {{123}, {4,5}};
Which looks absolutely fine to me.One of the other answers, which i agree is correct and so does the mock exam is
import java.awt.Color; import java.awt.GridLayout; import java.awt.event.ActionEvent; import java.awt.event.ActionListener; import javax.swing.*; public class Screen implements ActionListener { public JButton[][] b=new JButton[200][200];
[Code] ....
I am trying to create the A* Algorithm and I REALLY need a 2D array to handle this.
This is the error:
Java Code:
at java.awt.AWTEventMulticaster.componentShown(AWTEventMulticaster.java:162) at java.awt.AWTEventMulticaster.componentShown(AWTEventMulticaster.java:162) at java.awt.AWTEventMulticaster.componentShown(AWTEventMulticaster.java:162) at java.awt.AWTEventMulticaster.componentShown(AWTEventMulticaster.java:162) at java.awt.AWTEventMulticaster.componentShown(AWTEventMulticaster.java:162) mh_sh_highlight_all('java');
I am trying to program an A* algorithm and I cannot even get past the buttons. I need a 2D array of buttons to handle this problem but I am getting the following errors.
at java.awt.AWTEventMulticaster.componentShown(AWTEventMulticaster.java:162) at java.awt.AWTEventMulticaster.componentShown(AWTEventMulticaster.java:162) at java.awt.AWTEventMulticaster.componentShown(AWTEventMulticaster.java:162) at java.awt.AWTEventMulticaster.componentShown(AWTEventMulticaster.java:162)
class GVector { // TODO: declare a private array to save the vector coordinates // Creates a mathematical vector of d dimensions, initialized at 0 public GVector(int d) { // TODO: implementation
[Code] ....
I'm confused with what type of array I need to use to save the vector coordinates and what to put in Gvector. Is it a constructor?
I'm finishing up this assignment, and I'm stuck. These are the last 2 instructions:
. Roll each of the Dice by invoking the roll method on each Dice in the array. . Keep track of the totals sum of all the dice in the array. Be sure to roll the dice array at least 10000 times.
How to finish it up?
Here's my code so far:
package homework3;
import java.util.Random; public class Dice { private int numberShowing; private final int numberOfSides; private static final Random randomNumber = new Random(); public Dice() { numberOfSides = 6;
public class Person { private String name; private int age; public Person (String name, int age) { this.name = name; this.age = age;
[Code] .....
And I need to write a simple main method that creates lots of instances of the Person class and adds them to a generic instantiation of a Collection (ArrayList). And I need to make it so I as a programmer can define how many instances to create.
Where usually to instantiate and declare variables to be used in a loop. If you declare it outside to be used in the loop it will still be there when the loop is done, never to be used again and is just sitting there taking up memory. However, if you declare it inside the loop, you have the issue of it constantly creating space for said variable, but once it's out of scope it's gone. Is there any advantage performance wise to doing it either way?
Netbeans tells me it's an illegal start of expression during the initialisation of the interactWithUser method. public class InvertLetter {
/** * @param args the command line arguments */ public static void main(String[] args) { /** * String mit den Kleinbuchstaben. */ final String lowercase = "abcdefghijklmnopqrstuvwxyz";
Let's say within a class I create a method that takes care of creating a java swing layout with labels, buttons etc.. then attach an action listener (inner class) for each button to change a respective label text. All I would need is that the action listener method can access and modify the label as needed.
Have read about static, protected, private, getters and setters but honestly bit confused about which structure should be adopted as a best practice. Global static protected variables for the labels along with private inner classes implementing ActionListeners believe will do the trick and will be able to access the labels but not convinced this is good practice.
import java.util.HashSet; import java.util.ArrayList; public class Graph { double [] [] adj; graph (double [] [] a) { adj= new double [a.length][a.length]; for (int i=0;i<a.length;i++) for (int j=0;j<a.length;j++) adj[i][j]=a[i][j]; }
C:UserscDesktopGraph.java:: error: invalid method declaration; return type required graph (double [] [] a)
I'm new to Java and have been stuck on how to use a final declaration statement once it's made. Below is a class I'm creating with the intention of calling it under a main method. I don't understand if I'm supposed to do anything else, like do some sort of get/set, or if the final static line is all I need. And, I don't know how I call it to the main method once I do.
public class Shirt//class name. { int collarSize;//data field. int sleeveLength;//data field. public final static String MATERIAL = "cotton";//final data field for material.
I am not able to understand what does this URI exists at all ?? I feel it making things complex and meaningless or else i am missing something hidden and secret.
when a new object is created in Java it follows the idiom:
Object obj = new Object(); where the Object() constructor matches the object type Object.
But what if it doesn't? I understand from the Oracle Docs on creating objects and polymorphism that the constructor must be in that object's class or one of its subclasses. However, suppose we wanted to declare a new stack. My first instinct would be:
Stack s1 = new Stack(); But I assume it's valid to do it this way, too:
Object s2 = new Stack(); // Is there a difference here? What are we really saying about s2? I'm guessing s2 is simply an empty stack, but only has access to the Object class methods? I'm not sure why someone would ever do this, but I want to solidify my understanding of the Java hierarchy. Are there really any circumstances where someone would use a subclass's constructor when creating a new object?
I have one interface with three(more than one) method declaration. In the subclass that implements it I want to define only one method not all three not even blank definition of them.Is there any keyword or method for that. How to do it? Is it possible to do it? In GUI we use adapter classes to achieve it. What for console application?
What is exact difference between them? Another thing is when I check (a==b) it retuns me false, but when I check a.equals(b) it returns me with true. Why So?
I have an application that uses an object that is declared globally for the class. Within a method that is triggered by a user event, it creates a new object and assigns it to this global object declaration. My question is, when the object is overwritten multiple times by the user selecting the button that calls this method, will the older instances be garbage collected or is there still a reference to them? Is there any downfall to this logic and if so what would be a solution.
I have to implement all the stack methods in java such as push, pop empty, not using the ready methods but have to create them and to execute an exercise but is sth wrong with it
public class Stiva {
/** the problem is here how to declare the stack 1 and stack 2 and kreu(head) gjmax(size)*/
int Gjmax; int array[] = new int[Gjmax]; int kreu; private Stiva stiva1; private Stiva stiva2;
I have made a server/multi Clients where Clients send Double data but my problem is that the clients send this data to Server only wonce, and the server waits again the connection from client. (I have to run the clients manually each time)what i'm looking: the client should always send data to server. like an infinite loop.
