Test To See If Object Is Instance Of Interface Class
Mar 7, 2015
I am currently trying to use Junit to test a whole bunch of stuff. I almost have full line coverage but I am getting hung up on testing an if statement that consists of whether or not an object is an instance of another class. This class happens to be an interface, and even the object is an interface. Weird I know but I just want to know how to get into that if statement. I realize testing interfaces might be a waste of time but I still really want to know how. Here is an example of what I am trying to test:
Java Code:
if(x instance of y){ //where x and y are both interface objects
doSomething();
} mh_sh_highlight_all('java');
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Apr 14, 2015
I have been researching the Iterator and making a class implement iterable. I have seen this example shown below and was wondering how I could change this so that iterable() is not called upon in the main. I would like to be able to make a method that returns an instance of a class that implements the Iterator interface hopefully an inner class. This is because my program will not have a main and will be supplied with a main that includes a new Object with will use the iterator method.
import java.util.*;
public class IteratorDemo {
public static void main(String args[]) {
// Create an array list
ArrayList al = new ArrayList();
// add elements to the array list
al.add("C");
[Code] ....
This is all I have been able to understand from what I want to do. This does not work and this is what I am trying to achieve
public class MyArrayList implements Iterable {
public static final int DEFAULT_SIZE = 5;
public static final int EXPANSION = 5;
private int capacity;
private int size;
private Object[] items;
[Code] ...
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Nov 16, 2014
I am a beginner here at JAVA and I am trying to program a Gratuity Calculator using both interface class and object class but it keeps on compiling with errors saying "cannot find symbol".I tried everything to fix it but it just keeps on stating symbol.
[CODE]
public class GratuityCalculator extends JFrame
{
/* declarations */
// color objects
Color black = new Color(0, 0, 0);
Color white = new Color(255, 255, 255);
Color light_gray = new Color(192, 192, 192);
[code]....
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Jul 2, 2014
I have make the immutable class as below, Now my question is how I can test if my this class/object is immutable
package com.learning;
import java.util.*;
import java.util.Map.Entry;
public final class ImmutableTest {
private final int id;
private final String name;
private final HashMap<String, String> hm ;
[Code]...
How I can Test If it is immutable class without looking ?
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Jan 8, 2014
why interfaces inherit prototype of all the non final methods of the object class in itself? Object class is parent class of all the class and Interface is not the class.
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Apr 8, 2014
Suppose you have a generic Dog class of the pet type that implements a DogInterface of the pet type. What is the difference between;
DogInterface<pet> Rex = new Dog<pet>();
and
Dog<pet> Tye = new Dog<pet>();
In what situations might you want to use Rex instead of Tye?
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May 5, 2014
I'm just wondering why variables in interface can't be instance scope?
interface Test{
int a;
}
And then
Test test = new TestImpl();
test.a=13;
Yes, it violates OO, but I don't see why this is not possible? Since interface is not an implementation, therefore it can;t have any instance scope variable. I can't find the correlation of interface being abstract and being able to hold instance scope variable. There's gotta be another reason. I'm just curious about any programmatic limitation, not deliberate design constraint. the example of programmatic limitation is like when Java forbids multiple inheritance since when different parents have the exact same method, then the child will have trouble determining which method to run at runtime.
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Jul 13, 2014
I have been working on a program that is meant to use a class' instructions in a program to add a value to a variable, save it, and present it. This is my class
public class Car
{
//FIELDS
private int yearModel;
private String make;
private int speed;
//METHODS
public Car(int carYearModel, String carMake)
[Code] .....
Whenever I call the accelerate method, a value of 5 is to be added to the speed variable. But whenever I call accelerate, it doesn't increase! I just don't understand why not. I've tried different renditions of adding 5 to speed and it doesn't quite work. I don't get any errors when I compile, just runtime, when it doesn't add 5 to speed.
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Apr 7, 2014
So far in my assignment I have successfully opened a text file. However I am required to do more:
1) As each line of text (containing names and ages) is read a new Runner object is created with its instance variables set thus: ! (Runner class already created )!
- name : set directly set from the value in the file
- agaGroup : can be worked out from the given ages:
< 18 should be 'junior'
> 55 should be 'senior'
the rest should be 'standard'
2) the instance of Runner should be added to the list referenced by the instance variable runners.
I have used if statements to create the junior list, however I do not see the full list of names and ages in the variable runners as I am requested to.
I am sure there is a for loop involved somewhere but I do not know how to:
a) use the for loop in my method
add a new Runner object with the variable mentioned.
I include the code I have done so far as a file - p.s I use Bluej.
public class MarathonAdmin
{
// instance variables
private String runners;
private String age;
[Code] ....
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Feb 5, 2015
Let's pretend I'm working on an RPG. Like in all RPGs, there are items found all throughout the imaginary world. Each player and NPC can obtain an item. My question will concern those items.
In other words, I'd like to use instances of a class in multiple places of the code. Each instance will have its own, individual values of instance variables, with one obvious exception: itemQuantity should have a different value in playerInventory, npcInventory, etc. Also, I'd like a list of all items that can be found in the game. This list doesn't need itemQuantity at all.
class Items {
String itemName;
float itemWeight;
int itemQuantity;
[Code] ....
The question is: should I really make itemQuantity an instance variable of the Item class? It seems as though for each copy of the Item class I should create a separate copy with different value of itemQuantity, but that's not very efficient. Where is the error in my logic?
What's important is that there may be plenty items in a game and a player may be given power to create new items during the course of the game.
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Jul 5, 2014
I am working on a program that simulates a bug moving along a horizontal line, My code works correctly when I test it in it's own class but when I tried testing my constructor and methods in a test class I received an error saying, "package stinkBug does not exist" on lines with my methods. However, stinkbug is not a package.
Java Code:
/*
* To change this license header, choose License Headers in Project Properties.
* To change this template file, choose Tools | Templates
* and open the template in the editor.
*/
[code]....
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Oct 26, 2014
I can't figure out where to create the StringHandler object. My code should take a string as input, then create StringHandler object ord with the string input. This should repeat until cancel is pressed, then ord should be sent to the Utskrift-method (a print method).
If I do like this, null is also sent to Utskrift. I dont want that to happen.
If I put StringHandler last in the loop ord can not be resolved.
String text = "";
while (text != null){
text = showInputDialog(null, "Enter text:");
StringHandler ord = new StringHandler(text);
if (text == null){
[Utskrift(ord.getNumber(), ord.getString(), ord.getWords());
break;
}
}
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Jun 30, 2014
so, i was reading my java book and learning about objects and methods and it starts talking about Encapsulation and mentions that it's good practice to set instance variables as private and instead of accessing the instance variables directly, we should create a set method and get method to get and set the stuff we want to pass to the class containing the object...
for example, in this class, we're passing the integer 70 for object dog one and integer 8 for object dog two for the dog class... and these these 2 integers are sent to the setsize method so we're not accessing instance variable size directly.
i dont quite get it though....if we the programmer are the one deciding what size the integer is for the dog, and the setsize method takes the one.setSize(70) or (8) and puts them in setsize(int s) as s... but only to copy that integer stored in s back to private int size.... why do we even need to bother with making these two extra methods such as setSize, getSize?
in the book it says that... well what if the code gets into the wrong hand and someone writes something like one.setSize(0) then you would get a dog with size 0 which is essentially illogical. but then again, i'm the programmer, and i am the person who writes the code and passing the right integer.The reason for public and private... that part i understand... i can see why if a variable's data can get changed amidst the code during calculations and you dont want it to directly change the original variable and have it mess up the code, but this code from the book just a bad example of demonstrating the reason? since we manually pass the information ourselves and passing it to method setSize... and all setSize does is stores it in another integer, only to copy it right away to size (which is the original private variable we were tryign to protect?
Any simple code to demonstrate how the code might end up changing an instance variable and why we would want to protect it by using private?
class GoodDog {
private int size;
public int getSize() {
return size;
}
public void setSize(int s) {
size = s;
[code]...
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Feb 18, 2014
I have been writing test scripts for my class but I'm stuck on this method. how do i test for an object?
@Override
public boolean equals(Object obj) {
if (obj.getClass() != Fraction.class)
return false;
return (this.toString().equals(obj.toString()));
}
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Aug 9, 2014
Essentially, the code I want is:
public void randomCreate(ParentObject obj){
int x = random(0-4); //pseudo
int y = random(0-4); //pseudo
create new ParentObj(x,y);
}
ParentObject is actually abstract, so you would only ever pass one of its children objects to it, and a child object of that type would be created. It seems like there should be a way to pass a type, rather than an object, and then create an instance later down, but I don't know if that is actually possible, or if it is poor programming style.
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Mar 30, 2014
what have I done wrong n the following code? I'm trying to create a new instance carte of object Carti using the constructor and then to insert a row into a table created with SQL.The error I'm getting is:
Exception in thread "main" java.lang.NullPointerException
at Carti.Carti.InsertCarti(Carti.java:103)
at Main.main(Main.java:37)
Java Result: 1
BUILD SUCCESSFUL (total time: 28 seconds)
The line Main.main(Main.java:37) is when I try to insert the row.
The line Carti.Carti.InsertCarti(Carti.java:103) is when I do the
PreparedStatement st = conn.prepareStatement("insert into Carti (Id,titlu"
+ ", descriere, autor, editie, anPublicare) values (?,?,?,?,?,?)");
Here is the code (Main and Carti Classes)
import Carti.Carti;
import Imprumut_Carti.Imprumut_Carti;
import Membrii.Membrii;
import static com.sun.org.apache.xalan.internal.lib.ExsltDatetime.date;
import static com.sun.org.apache.xalan.internal.lib.ExsltDatetime.date;
import java.sql.SQLException;
import java.text.DateFormat;
[code]....
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Aug 6, 2014
I'm having trouble understanding the concept of the interface Connection, and PreparedStatement.
1) The simplest way to put it is how is it possible that this code is creating Connection and PreparedStatement objects? I was always under the impression that interfaces cannot be instantiated, but rather implemented. For example I don't see "public class Prepared implements Connection", or "public class Prepared implements PreparedStatement", But I see "Connection con = null;" and "PreparedStatement pst = null;". So it seems as if the interfaces are being used to create objects called con and pst.
2) If in fact these interfaces are being implemented, where are the method blocks in this code that should have been added in order to fulfill the contract?
package zetcode;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.SQLException;
import java.util.logging.Level;
import java.util.logging.Logger;
[code]....
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May 5, 2014
Whenever i perform any operation in my application Live Bytes of a particular Instance of a class increases by 1000.Although i perform the same operation everytime it always increases by 100 or 1000.Is this a memory leak or does these instances increase everytime we perform an operation.
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Feb 7, 2014
I am trying to test the instanceof keyword. To do this, I've made a method with a simple logical test like so:
Java Code:
Vehicle vehicle1 = new Vehicle();
public void Type(){
if (vehicle1 instanceof Vehicle) {
System.out.println("Type = Vehicle");
}
else if (vehicle1 instanceof Car) {
System.out.println("Type = Car");
}
else if (vehicle1 instanceof Truck) {
System.out.println("Type = Truck");
}
}
} mh_sh_highlight_all('java');
I wanted to try implementing it into the class definitions for Vehicle, then extend that to Car and Truck, but I'm not sure how to use this test in a general case.
The only way this method works is if I set the test to specifically accept a specific object as a parameter.
I want to test multiple objects, but I'm not really sure how else to do this without simply copy-pasting the logical test multiple times and changing the respective objects that are used as parameters.
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Mar 3, 2014
What does the iterator() method return???it can't return an object of Iterator as it's an interface...
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Aug 5, 2014
jboss 7.1.1
EJB 2.1
Though it may seem strange but in one of the application i work on still uses EJB 2.1 entity beans.While looking at the deployment log, seems like each Entity bean is registered using both remote-home and remote interfaces.
java:app/EJBApp/Entity!com.abc.remote.Remote
java:app/EJBApp/Entity!com.abc.remote.RemoteHome
Using the remote-home's JNDI lookup i was able to get the EJBObject proxy and subsequently create and use the entity.But what about the remote interface JNDI lookup ? Reason i am asking is that one needs to create an entity before use it. That said, how to use the object that i get from remote interface JNDI lookup ? Note that the class of the returned object says its "com.sun.proxy.$Proxy13" type.The JNDI location i am using "java:app/EJBApp/Entity!com.abc.remote.Remote"
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Dec 13, 2014
Assuming that we have two classes B and C which inherit from class A. What is the best way to pass a parameter from an object of class B to an object of class C by the use of class A without using static variable and without defining a get function in B?
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Sep 25, 2013
Can I declare a class as
public static final?
Because I can declare a variable as public static final pi=3.14;
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Mar 22, 2014
Java Code:
package Threads;
// THIS PROGRAM WILL HAVE TWO THREADS i.e. "main" AND ANOTHER THREAD (SYSTEM WILL NAME IT "Thread-0"
//THE STORY IS THAT WE WILL START Thread-0 FROM main AND LET IT EXECUTE.
//main WILL WAIT AND LET IT EXECUTE FOR 5 MINUTES.
//IF IT FINISHES ITS EXECUTION BEFORE 5 MINUTES, WELL AND GOOD;
//BUT IF IT DOESN'T, WE WILL INTERRUPT IT.
//AFTER INTERRUPTION, WE WILL DECIDE TO WAIT INDEFINITELY.
public class SimpleThreadsCopy {
public static void threadMessage(String s){
String sThreadName= Thread.currentThread().getName();
System.out.format("%s: %s%n", sThreadName, s);
[Code] ....
The statement against which I have written many *'s gives the following error.
No enclosing instance of type SimpleThreadsCopy is accessible. Must qualify the allocation with an enclosing instance of type SimpleThreadsCopy (e.g. x.new A() where x is an instance of SimpleThreadsCopy).
Now that a similar "error-free" code is given here, what's wrong with this piece of code and what should I do about it?
Trying to understand the error statement, I replaced the erroneous statement with
Java Code : Thread t= new Thread(new SimpleThreadsCopy().new MessageLoop()); mh_sh_highlight_all('java');
And the error got fixed. From that I understand that the inner class is just kinda a nonstatic member of the outer class and it will be accessed by the objects of the outer class only.
But then why doesn't the code in the tutorial give an error?
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Mar 25, 2014
I'm having trouble to fully understand the difference between instance and class variables.
I though it was all about the static, i.e:
int age; // instance variable
static int age; // class variable
What's behind this?
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Mar 15, 2014
So in the code below I create an instance of my own triangle class and use one of its methods. The thing is I use one of my triangle classes methods in a method other the main method of my main program so I'm thinking it can't access it?
Any way here's the code for my triangle class
import java.util.Scanner;
public class QudratullahMommandi_Triangle_06 {
Scanner keyboard = new Scanner(System.in);
private double side1;
private double side2;
private double side3;
[Code] ....
and here's the error message
QudratullahMommandi_S_06.java:46: error: cannot find symbol
{ triangle1.outPut();
^
symbol: variable triangle1
location: class QudratullahMommandi_S_06
1 error
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