I have the following 2 classes:
class Address {
private int a;
public void set_a(int a) {
this.a = a;
}
}
class Person {
private Address address;
}
How do i access the method set_a() (through the "address" in Person) from another class which contains main() ?
I am having some problem accessing variables from an array instance of a class. Heres what i have done;
In the main class:
Example obj[]= new Example[4];
In the main class constructor:
obj[0] = new Example(0);
obj[1] = new Example(1);
obj[2] = new Example(2);
obj[3] = new Example(3);
In the main update() method:
if(condition)
//update
In the Example class constructor:
private boolean change = false;
In the Example class update() method:
if(x >20)
change= true;
Now, i want to access the variable change from the main class, how do i do it? The 'condition' in the if statement is the condition of wether the change variable ia true or false. How do i access it?
Do inherited methods use their instance variables or do they use the ones in the method that inherits them?
For example, Class B extends Class A. Class A and B both have the instance variable "potato". A client program tries to use method "cut" using an object of Class B, but class B has no cut method. So, class B uses the "cut" method inherited from class A. What I want to know is will that cut class A's potato or class B's?
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]...
I thought static methods could never use instance variables, because they wouldn't know which instance to look at.
From Head First Java, p. 284: "A static method is not associated with a particular instance - only the class - so it cannot access any instance variable values of its class. It wouldn't know which instance's values to use."
Now I was answering some mock exam questions from Cameron McKenzie's SCJA book, and I don't understand one of the options. On page 205, the last question has an option that says: "Instance variables ... are not visible in static methods, unless passed in as arguments." This option is supposed to be correct. Now... how does that work?
I have 1 textfield and 1 button on a JFrame and having 10 such frames stored in ArrayList al and getting the JFrame instance from traversing the ArrayList at execution time ,So is there a way to access textfield using JFrame instance or i have to name the textfield diffrently 10 times for each frame .
View Replies View RelatedI wanna know which is the best way to access a variables within a class ...
Using direct access or using the variable accessor ...
Example :
public class Numbers{
private int n1;
private int n2;
public void setN1(int n){
n1 = n;
[Code] ....
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] ....
When I input "the" or "and" I always receive "its not here" as the output. Why is this? I also tried printing the values of v.get(i).other and the system printed null twice.
public class Translator {
public String other;
public Translator(String x) {
x = other;
[Code].....
While reading head first java i encountered a problem(Pg. 90 chapter 4 - mixed messages).
Suppose in a class(say A) outside main() a counter variable is declared and initialized to 0.
In main() declared the array of objects of the class A.
Consider a while loop in which we increment the counter as follows:
public class A{
int counter = 0;
public static void main(String[] args){
A[] arr = new A[20];
int x = 0;
while(x<4){
arr[x] = new A(); //arr[] is array object
arr[x].counter += 1;
x++;
}
}
};
what is the final value of counter ? will it be the same for all array objects.
What is the correct way of describing the type of instance variables?
It is obvious in the case of a primitive type
Example: private int number;
The (data)type of number is integer.
What if the instance variable is an object or a wrapper?
example: private Person person;
the (data?)type of person is an object of the type/class Person?
example: private Integer number;
Suppose I have private static void name() { ... } that has a two dimensional string array named array[. Now suppose I have private static void different() {...} and I want to write a condition where if (item == array) { ... }, how can I access my array from name() when I am in different()? I get a compile error saying cannot find symbol. My code is similar to:
Java Code:
public static void main(String[] args) {
...
String item = keyboard.nextLine();
... }
private static void name() {
...
String[][] array = new String[1][5];
[Code] .....
why overridden doesn't apply to variables. However, instance variables are stored inside the object.I ran below program and expected to print "two" but it gets printed "one".
class SupCont {
String s = "one";
}
class Cont extends SupCont {
public static void main(String a[]) {
String s = "two";
SupCont c = new Cont();
System.out.println(c.s);
}
}
I have to create an application that deals with maps.
I first have to create the instance variables for the class.
So very simply if my hashmap is going to consist of football clubs and players. Football clubs being a string value for the key and players being a set of strings for the values. How would I go about creating the instance variable in a class for this?
I can't seem to find anything that specifically deals with instance variables and constructors for maps.
I am suppose to create a rectangle and I have created two classes; Rectangle.java and RectangleTester.Java.
So far my code for the class Rentangle.java is:
package edu.sbcc.hw2;
public class Rectangle {
private int width = 25;
private int height = 25;
public rectangle(int xcoord, int ycoord, int thewidth, int theheight) {
this.width = width;
this.height = height;
}
public int getWidth() {
return width;
So for my assignment I need two instance variables for height and width for which I have, but it says in the assignment I need methods (settings and getters /mutators and accessors that allow manipulation of my instance variables which is a little confusing. Do I put these methods on Rectangle.java or RectangleTester.java.
The same goes for the calculateArea, where am I suppose to put this?
From the tutorial:instance variables can be declared in class level before or after use.But the code below does not compile. Why?
Java Code:
public class MainApp {
i=5;
public static void main(String[] args) {
System.out.println("Hello World");
}
int i;
} mh_sh_highlight_all('java');
Creating a class. Specification are given as:
Create a class called Employee that includes three pieces of information as instance variables:
-Employee ID (string type)
-first name (string type) (default value 'John')
-last name (string type) (default value 'Smith') and
-monthly salary (type double).
-No argument constructor that initializes the three instance variables. The employee id should be generated using the following process:
The employee id should be a combination of first initial, last initial and a number starting from 10001 for the first employee and increasing by one for each employee. e.g. if John Smith is the first employee then its id will be JS10001 and if George Brown is the second employee then its id will be GB10002
-Provide get and set methods for each instance variable. The set method for monthly salary should ensure that its value remains positive - if an attempt is made to assign a negative value, leave the original value.
As web server has multiple threads to serve client requests in Thread Pool & to ensure Thread Safety we should not use any variables or Objects at Instance/Class level.But in case of Session Variable which one is the Best Practice as the Session object is used by all the requests to have the same Session ID.
My Code :
public class MyServlet extends HttpServlet {
private static Logger log = Logger.getLogger(ClientRegistrationServlet.class);
private HttpSession session; /* This is used at Instance Level*/
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
[code]....
Scanner in = new Scanner(System.in);
ArrayList<rand> selectedRand = new ArrayList<Rand>();
selectedRand.add(new Rand(in.nextLine()));
I have created the most minimal code for creating an array list. I was wondering what the basic syntax of accessing objects methods that are within an Array List. So if I was to trying and get a method such as [.returnValue,] how would this look within a Rand object that is declared in a Array List Since you cannot simply declare a new Rand object and say:
newRandObject.returnValue();
And you must go through the actual slotted portion of the array list. I have searched the web and my text book for an example however none are provided.
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
Okay, so I have to create a class with instance data and instance methods.
First, BankAccount class. It should contain the following information, stored in instance variables:
First name: The customer's first name.
Last name: The customer's last name
Balance: The amount of money the customer has in the account.
It should have the following methods:
BankAccount(String firstName, String lastName,
double openingBalance)
This constructor creates a new BankAccount
public String firstName()
Returns the customer's first name
public String lastName()
Returns the customer's last name
public double balance()
Returns the customer's account balance
Finally I need to create a driver to test my class. And create several accounts and verify that the first name, last name, and balance methods work properly. This is my code below.. I don't know if I did it right.
public class BankAccount {
String firstName, lastName;
double balance;
public BankAccount(String firstName, String lastName, double balance) {
[Code] .....
I've tried a couple ways to do it, and they don't work. I'm aiming for functionality like I got with the regular for loop, but from an enhanced for loop. Is this simply beyond the scope of an enhanced for loop, or am I just not getting the right syntax?
TestObject to1 = new TestObject("first", 11);
TestObject to2 = new TestObject("second", 12);
TestObject to3 = new TestObject("third", 13);
TestObject to4 = new TestObject("fourth", 14);
TestObject to5 = new TestObject();
List<TestObject> testList;
testList = new ArrayList<TestObject>();
[code]....
The TestObject class is simply an int and a String, with getters getInt and getString. It all works fine with the regular for loop.
edit: I should probably mention that I know what I have in the enhanced for loop now will only display the class name and the hash. I've tried adding the .getString and .getInt, and tried a few other ways to make it work. I just reverted to this because it compiles and runs
I have to make two classes. The first one crates an instance of an array of several integers and prints data (average, greatest, lowest, et cetera) based on the second class, which contains the methods. I'm having a problem with the syntax for the first class required to use the methods.
Here's a shortened version of what I have right now just based on processing the number of integers in the array (because if I can get just one method properly connected, I could figure out everything else).
Driver
import java.util.Arrays;
public class ArrayMethodsDriver
{
//Creates the ArrayMethods object
public static void main(String[] args)
{
int[] a = {7,8,8,3,4,9,8,7};
[Code] ....
When I try to compile this, I currently get the "class expected" error on the count part.
I'm making a java program that can "convert" java to arduino by sending commands over a serial port. I'm using the JSSC library, and using methods to shorten things up a bit.
I've already made the code that starts up the serial port and it does connect. But I've made two different classes for the methods. One for the RXTX and one for the Arduino.
I'm making it so that I can just type:
Java Code:
public static void main(String[] args) {
RXTX.SerialSetup();
Arduino.pinMode(2, 0);
} mh_sh_highlight_all('java');
And it will start the serial port and set pinmode on pin 2 to output.
But when I try it I get this error:
Java Code:
Exception in thread "main" java.lang.Error: Unresolved compilation problems:
serialPort cannot be resolved mh_sh_highlight_all('java');
I don't know if its possible to 'send' a variable to a different method.
i'm trying to modify and use a GUI to set the variables the setter methods. while the code seems valid to me and should work perfectly, i get ArrayIndexOutOfBounds and StringIndexOutOfBounds and respectively lines 111 and 134. i'm am not the original author of this code, all i want is to get it to work fine.
1package de.kugihan.dictionaryformids.dictdconv;
2
3import java.io.FileOutputStream;
4import java.io.IOException;
5import java.io.OutputStreamWriter;
6
[code]....
i need to change my code in order to stop the member variables from being directly altered and its been suggested that i should use a setter and getter method. Ive read up about these and im still unsure at how they should be implemented into my code for my project.
import ddf.minim.*;
DragShape[] piece =new DragShape[77];
PImage puz16;
PImage frame;
PImage text;
[code]....