I know in C++ It's possible to pass by reference but what about java?
For example, can i pass the address of a health variable into a Ninja class and then
Since Ninja inherits from an enemy class pass the health into the enemy class and within there have a function that returns that same health address and takes 5 from the health returning 95.
Primitive arguments, such as an int or a double, are passed into methods by value. This means that any changes to the values of the parameters exist only within the scope of the method. When the method returns, the parameters are gone and any changes to them are lost.
Reference data type parameters, such as objects, are also passed into methods by value. This means that when the method returns, the passed-in reference still references the same object as before. However, the values of the object's fields can be changed in the method, if they have the proper access level.For example, consider a method in an arbitrary class that moves Circle objects:
public void moveCircle(Circle circle, int deltaX, int deltaY) {
// code to move origin of
// circle to x+deltaX, y+deltaY
circle.setX(circle.getX() + deltaX);
circle.setY(circle.getY() + deltaY);
// code to assign a new
// reference to circle
circle = new Circle(0, 0);
}
Let the method be invoked with these arguments: moveCircle(myCircle, 23, 56)
Inside the method, circle initially refers to myCircle. The method changes the x and y coordinates of the object that circle references (i.e., myCircle) by 23 and 56, respectively. These changes will persist when the method returns. Then circle is assigned a reference to a new Circle object with x = y = 0. This reassignment has no permanence, however, because the reference was passed in by value and cannot change. Within the method, the object pointed to by circle has changed, but, when the method returns, myCircle still references the same Circle object as before the method was called.
I am unable to understand the meaning of this sentence "final reference variables must be initialized before the constructor completes.",What is trying to imply?
View Replies View Relatedif there is a possibility to use the pass by reference technique in java like in C++.URL....
View Replies View RelatedI got a project at my university , and we are working with JBoss with the free version WildFly .And also with Java EE.
Now the application is a simple game of Battle Ships or sinking ships to be honest i am not sure as to how the game is actually called.
Registering a user and saving his or her information is not hard using a Stateless java bean , to save the data in the database.
I have a Stateful java bean for every user , the bean is created on the server side after the user succeeds in logging in to the game.
This bean is used mainly for sending an invite from one user to another , to log out the user and everything else that is needed for the user.
The main problem that i encountered here is that JBoss dose not let me have a reference on my frame inside of the bean.
This makes things hard because i would need to use a Timer to ask the bean every second or so if there is an invite from someone , and i would need to save all of the invites .
This was the only thing i could think of .And also implementing the game it self , the communication between users would be complicated more so than i think its needed.
Then my professor said that i could make a service on the clients side in witch i would have a reference of the JFrame , and i could send this service to the java bean and using this service i could get access to the JFrame making things faster.
This would make things a lot easier.For the invite and for the game itself too.
My professor explained that JBoss or WildFly is based on RMI , and he said also that i would need to set up the registry on the server side .But i got lost because i was not sure as to what should i search for .
We are using an older version of WildFly not the newest but one version older , CR1 i think.
And we are also using JPA in the Dynamic web project , server .
I am trying to run the queue operations in java such as enqueue, dequeue using pointers ... How to use references as pointer in java.
View Replies View RelatedI faced with a problem, when I use method reference as a function in Collectors.groupingBy I get an error: "no suitable method found for collect". But! if I replaced method reference with a lambda expression everything works fine.
Here is the code sample:
interface Iface{
public int getPropertyOfClassA();
public void setPropertyOfClassA(int propertyOfClassA);
}
class A implements Iface{
private int propertyOfClassA;
[Code] ....
Change "C::getPropertyOfClassA" with "objC -> objC.getPropertyOfClassA()" and it works!
you will be making four variables (2 primitive integers and 2 Account Objects). You will be following the steps detailed below. The challenge is to understand exactly what is happening and why. Start by coding the following two methods in a java file.
Start your main method with four variables: a, b c, d. a and by should be integer data, set them to be the values 10 and 20 respectively. Variables c and d should be Account Objects. The first account © is Ted, has $70,000 as his balance. The second account (d) is Joe, he has only $15,000 as his balance. Their account numbers are up to you to determine.Next, please print out the four variables: a, b, c, and d. Make sure that you label which ones are which. After you print these variables, please pass all four variables to a static method that you will create below. After you finish the method, please print out the four variables again: a, b, c, and d. Just as they were printed before the method.
Static methods: This method can be called whatever you want, however it will be public, static, and void. This method should take in four parameters: w and x which will be integers, then y and z which will be Account Objects.The first thing this method should do is to print out the four variables w, x, y, and z. This should be done in the same manner as you did in the main method. Next, change the first variable (w) to 15. After that, ted bought a new car. He now has only $20,000 in his account. Change the balance of y to be 20,000. Step three is to make a new Account Object named John, he has a balance of $10,000. Assign him to the variable z. Lastly, print all four variables again: w, x, y, and z.
Java Code:
createConnection();
try{
String str = "select * from Stocks";
stmt = conn.prepareStatement(str);
ResultSet rs = stmt.executeQuery();
while(rs.next())
jcbStock.addItem(rs.getString("stockID"));
}catch(Exception e){
e.printStackTrace();
} mh_sh_highlight_all('java');
I want to put this code in a class then call it in another class , but i do not how to do that. This code is working fine in my main class , but i want to write this code to another class for call it in main class.
Here I am taking response data from JSON using jackson API.I found a feature like using Jackson the properties can be set to bean properties.
private static String readUrl(String urlString) throws Exception {
BufferedReader reader = null;
try {
URL url = new URL(urlString);
reader = new BufferedReader(new InputStreamReader(url.openStream()));
[Code] ....
I got the correct output here. But now I want to generalize my method into a utility class so that I can reuse the same method for setting response data directly to respective beans as given below:-
My question is how will I pass the bean object in my utility class?
public static Object getResponseData(String response,[b]String bean[/b]) throws Exception {
ObjectMapper mapper = new ObjectMapper();
mapper.configure(DeserializationConfig.Feature.FAIL_ON_UNKNOWN_PROPERTIES, false);
JsonNode root = mapper.readTree(response);
[Code] ....
currently I am doing my java web application project ,and it has following steps 1) Upload the txt files 2) java servlet gets the txt file's url , read the data and do the calculation 3) pass the results
I almost finished the second step , and working on the first step .Since there are so many input files at a given time , i have to use drag and drop method to get the file's location.how to pass file's path to servlet.( servlet code can read the data from the given txt file path )software used - tomcat and netbeans 8.0
I am doing a Junit test case, but I keep having issues with AssertEquals ( object expected, object actual). I don't know how to reference the other actual object so that it can compare to the expected.
public void add (Distance d) throws CustomException
{
//I can also convert feet to inches and add all inches together and then divided inches to feet and inches
Distance result = new Distance();
int newFeet = this.feet + d.getFeet();
int newInches = this.inches + d.getInches();
if(newInches > 11)
{
newFeet = newFeet + (newInches/12);
[Code]...
I don't really know what this means and it is sending an error when I try to run my program I am trying to set the x and y value (Int x and int y) to setVisible false at a specific time in my game but it keeps sending the error that int is not a reference type.
View Replies View RelatedI'm fairly new to Java, I'm very experienced with C++ and C# in which you can pass by reference - extremely useful. Take for example this bit of code in C#:
class MyClass
{
public MyClass(int i)
{
m_i = i;
}
public int m_i;
[Code] ...
Just at the end of this program x.m_i will be equal to 8. As far as I can see this is not possible in Java: you can't pass a double by reference, using a Double will kick in the autoboxing so that won't work either. The only "solution" in Java would be to pass in a double[] (of length 1) or to make a wrapper class, both nasty solutions because a user may want to just hold a double as a member of their class just as I have, for reasons such as not allocating more memory for a class and generally not being bloated.
I am making an MVC program and I am not allowed to put the action listeners in the view class. I was able to get one button working fine but since I am unable to reference them I cannot give them both individual responses.
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
public class Controller {
HobbyList model;
ListView view;
[code]....
public class {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
double[] numbers = new double[10];
System.out.println("Enter " + numbers.length + "numbers");
for (int i = 0; i < numbers.length; i++) {
numbers[i] = input.nextDouble();
[Code] .....
I am trying to reference the input "numbers[i]" to my mean method, how do i do that?
I passed my abstract class private final reference to another concrete class and I used abstract class reference as parameter to that concrete class constructor and in my main method and null to that parameter then only that program executes correctly...i placing my code below ..if there is any error tell me where is error occurring then i will check my code...i think my code is right but little bit doubt abstract class concept.
{
}
class concept1 extends concept
{
private final concept parent;
public concept1(concept aparent)
{
parent=aparent;
System.out.println(parent);
}
public static void main(String args[])
{
//concept p=new concept1(null);
concept c=new concept1(null);
}}
When I write a statement such as:
myType x;
This means that x is a reference to objects of type, "myType" and no memory has been set aside for an instance of this object. I think it's true that x also has the starting memory address of this object.
What I feel uncertain about is if x is telling the JVM(?) where it can find the starting address of this object, why do we care about the type that x is?
i.e., if we assign x to an object totally unrelated to this type then the compiler would complain - correct? If so, how come, since all x is doing is telling the JVM(?) where to find your object (via the address it contains).
I suppose all, hy a reference has a type associated with it if all the reference does is point you to the object?
I am currently learning Java basic concepts and this is a very simple code which produces error depending on the way I write. It is as follows:
package testPackage;
interface ArrayInsideClassShock {
}
class Check{
ArrayInsideClassShock var[]; //Error line
var= new ArrayInsideClassShock[10];
}
Error in eclipse:Syntax error on token ";", , expected
But if I write it as:
package testPackage;
interface ArrayInsideClassShock {
}
class Check{
ArrayInsideClassShock var[]=new ArrayInsideClassShock[10];
}
It doesn't show any error.
what these mean with examples..
1. A reference variable can be of only one type and once declared, that type can never be changed(although the object it references can change)
2. A reference is a varaible ,so it can be reassigned to other objects(unless the reference is declared final)
3. A reference variable's type determines the methods that can be invoked on the object the variable is referencing.
4. A reference variable can refer to any object of the same type as the declared reference , or - it can refer to any subtype of the declared type.
5. A reference variable can be declared as a class type or an interface type. If the variable is declared as an interface type, it can reference any object of any class that implements the interface.
I don't understand why following code when executed returns false
String s1= " string".trim();
if(s1 == "string"){
System.out.println("true");
}
else{
System.out.println("false");
}
How can i check the reference that is not duplicate and date format is DDDCCYYnnnnnnn, CC must be 20 and YY must not be less than the current year, nnnnnnn is the sequetial number of the file and to complete the 7 numeric characters, zero's must be populated in front of the number. DDD must be a valid reporting entity code. there must not be a duplicate. Code I try
private boolean test-date()
{
String s_Ref = this.transactionFile.getsReference();
boolean flag = true;
if(!isValidPattern(s_Ref, "[0-9]{14}"))
[Code] ....
The reference number is like 201401030234509
If there is duplicate show error code 105
I have started working on a little project in my free time. It is just a simple text rpg that runs in a counsel window. I have 5 files each file contains 1 class.
public class SomnusCharacter {
private String gender = "";
private int age = 0;
private String race = "";
private int level = 0;
private int xp = 0;
[Code] ....
The chain of events right now is:
1. MainMenu is run
2. If user inputs n CreateCharactor is run
3. User inputs name, age, ect in SomnusCharacter object made in CreateCharacter
4. Intro (just rough demo for testing purposes) is run
5. If user inputs m Menu is run
6. Menu calls and prints out all the information from the object made in CreateCharacter
Step 6 is where I am having my problems. How can I reference (lets say the SomnusCharacter object made is called player) player from my Menu class? I know that if I made a new character that it would just create another SomunsCharacter object with the default values again.
I read somewhere : "Java use clone() method of Object class to copy content of one object to the other. The problem will arrive if the Class that needs to be copied also contains reference to the other object."Not able to understand the second line.
View Replies View RelatedHow are methods invoked on the `bird` parameter?
next.xhtml:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml"
xmlns:ui="http://java.sun.com/jsf/facelets"
xmlns:h="http://java.sun.com/jsf/html"
xmlns:f="http://java.sun.com/jsf/core">
[Code] ....
`MyQueueBean` is intended to give out a bird once only, to exactly one end-user. Because it's application scoped, and not session scoped, getting attributes directly from the bean would give inconsistent results.
The birds application is from Facelets Essentials Guide to JavaServer Faces View Definition Framework: [URL] ....
how is the variable passed to the file? Once it's passed, how is it referenced?
Is there a short term that means: "using an object reference with the datatype of a supertype to refer to an object with the datatype of a subtype"?
Saying "polymorphic reference" doesn't seem to be specific enough because ALL references other than those with the Object datatype are polymorphic. I saw one post that referred to these reference variables as a "supertype reference." In the absence of any other (more official) term, I may just use that term because calling a reference a "supertype reference" implies that there is a subtype. It sure beats what I was thinking about using: "sub-as-super." Which, when the inevitable mispronunciations occur, would lead to all kinds of off-color jokes.
Is there an "official" term that all of the dozens of Java books I have read seem to have missed? Or does everyone stumble along, spelling things out with a nearly sentence-long phrase.