I think its a standard concept but just not getting it. I have 3 classes:
1) Base class
2) Derived class, which extends base
3) TestClass
public class Base {
public void display() {
System.out.println("Display method in Base");
}
}
class Derived extends Base {
public void display() {
System.out.println("display method in Derived");
[Code] .....
So if i run this, my results are:
Display method in Base
display method in Derived
display method in Derived
Thats cool, no problems there, but if i change my Display method in Base and Derived to static methods then the results become:
Display method in Base
display method in Derived
Display method in Base
So why oh why does obj3.display() now print "Display method in Base"?
(and yes I know the calls should be static calls, but for sake of arguments -- or is that the whole problem, that technically obj3.display() is an incorrect call as it can only be Base.display() or Derived.display() when display() is a static method ).
If i have 2 classes, Top and ClassB which extends Top
public class Top { String variable; public Top(){ setVariable(); } void setVariable(){ variable = "variable is initialized in Main Class";
[code]....
So what is happening when ClassB inherits from Top?I know that the B constructor is calling super, so does that mean its calling setVariable (in Top?) but as its overridden in ClassB, then that is whats being called and setting the String variable?
I have a multithreaded application. I have a Logger class with static methods that I use across threads. Would it behoove me to add the synchronized keyword to the static methods of the Logger class since I use this class statically in different threads?
If I define a class which contains a few static fields, and then have a few classes who inherit this class, then all these classes would have the static field as well. Now my question is the following: would all those sub classes (and the base class itself) share the same object, or would each class have one object for all it's instances?
I have two classes (Daughter and Son) that contain some very similar method definitions:
public class Family { public static void main(String[] args) { Daughter d = new Daughter(); Son s = new Son(); d.speak(); s.speak();
[Code] .....
Each of those classes has a "speak" method with two out of three lines being identical. I could move those into a parent class, but I need each of the child classes to continue to exhibit its unique behavior. I'm trying the approach below, which replaces the unique code with a call to a "placeholder" method that must be implemented by each child class:
public class Family { public static void main(String[] args) { Daughter d = new Daughter(); Son s = new Son();
[Code] .....
This works and moves the shared code from two places (the Daughter and Son classes) into one place (the new Mother class, which is now a parent class of Daughter and Son). Something about this feels a bit odd to me, though. It's one thing for a child class to override a parent class's methods to extend or alter their behavior. But, here, I've implemented an abstract method in the parent class to alter what happens when the parent class's method (speak(), in this case) is called, without overriding that parent class method itself.
I use this code in Restlet Representation. I try to get the value from the Request API. But I am facing the problem as "Cannot make a static reference to the non-static method getQuery() from the type Resource".
From what i understand static methods should be called without creating an instance of the same class . If so why would they return an instance of the same class like in the following : public static Location locateLargest(double[][] a) , the Location class being the same class where the method is defined . I don't understand this , does it mean that every field and every method in the class must be static ? Meaning that you cannot have instances of the class because everything is static . Or it's just a mistake and the class Location cannot have a static method: public static Location locateLargest(double[][] a) ?
I can't figure out what this error message "Cannot make a static reference to the non-static method getEndUserCharge(long, long, long, long) from the type UpdateUserWS" actually means.
The error is coming from:
public void updateDetailsPackage() { some unrelated code long zero=0; double endUserCharge=0; endUserCharge = UpdateUserWS.getEndUserCharge(long zero, long zero, long zero, long zero); <-------- error is here
I'm working on a banking program that is supposed to use 3 classes (Account-base class, CheckingAccount, and SavingsAccount) and several methods to display the banking information (ID, balance after a withdrawal and deposit, and the annual interest rate). This should be a pretty simple program, but I'm getting hung up on one portion of it. I'm getting some compiler errors, all of which deal with non-static variables being called from a static context (I'll also post these errors following the code). Up until the middle of last week, we just declared everything as static, but that's changed and I'm having trouble figuring out when to and when not to use static when declaring my methods, hence the compiler errors.
import java.util.Date; public class Account { private int id = 0; private double balance = 0; private double annualInterestRate = 0; private Date dateCreated = new Date();
[Code] ....
Here are the compiler errors I am receiving:
Compilation completed. The following files were not compiled: 6 errors found: File: C:UsersHiTechRedneckDesktopSummer II 2014Computer Programming PrincipleProgram 5CheckingAccount.java [line: 7] Error: non-static method getId() cannot be referenced from a static context
I am trying to calculate a fine in a PoliceOfficer object with method calls to a ParkedCar and ParkingMeter object. The word problem is:
The fine is $25 for the first hour or part of it and $20 for every additional hour of part of it.
My code is:
public class PoliceOfficer public static final int PARKING_FINE1 = 25; public static final int PARKING_FINE2 = 20; public static final int NUMBER_OF_MINUTES_OVER_PARKED = 60; public double calculateFine(){ double calculateFine = 0;
[Code] ....
obviously the fine is not calculated correctly but I'm not sure how to proceed from here...
I had a TestColor class which contained methods to change hue, saturation, brightness, red, green, blue of TestColor's instances but also had static methods which take in an additional parameter for an instance of TestColor and returns the affected instance of TestColor. Now instead of having one method for every possible color effect to be applied to an image, how can I have one method that takes in an Image parameter, a static or non-static method reference from TestColor parameter and lastly an intensnity value parameter. This is so that I can make an affectedImage object instance inside the method and a Graphics2D object for drawing to each pixel of the new image, now I have one for loop and one nested for loop for the x and y pixels of width and height of the old image and inside the nested for loop I'd create a TestColor by calling getRGB on the image's pixel. Then I would apply the static or non-static method reference somehow to change the color with the intensnity value and after applying it draw to the new Image with Graphics2D. How to would I parametize a method reference and be able to use it in such way?
One class having two method one as static n another as non-static, 2 threads are there t1 is accessing the static method and t2 the non-static method is it possible n both are sharing the same object.
I now we have two kinds of lock one is object level lock and another is class level lock
I am trying to compile the following code where the entry point is Main.java but i am getting the following error "Error non-static method add(int[]) cannot be referenced from a static context in Java " ....
If i add the keyword static in add method of A.java it works properly......
Class Main.java code package com.company; public class Main { public int [] a= new int[]{1,2,3}; public static void main(String[] args) { Main n= new Main();
I am trying to use method calls with returns but it keeps on showing errors. The errors say class, interface, or enum expected. I realize this error occurs if there is issue with declaring class - but i can't seem to find the error. I will post the code that shows error.
import java.awt.*; import java.awt.event.*; import javax.swing.*; import java.text.*; public class FuelCost extends JFrame { // declarations Color black = new Color(0, 0, 0);
class test { static int i=j; static int j=10; .....
this will give illegal forward reference ....
but this will compile successfully ..
class test { static int i=test1(); static test1() { return 20; } } .....
plz assume we have main method in both cases ..
java would be loading all static members first and would be assigning default values .. and then will be running all the initializers from to bottom ..Why second case is a compile success and not first .. as in second also test1 method is declared after its usage ..
I'm writing a program that calculates phone charges. I have my class is set up, but when I try to retrieve data from it in my main, eclipse says that I need to set my method to static, which messes up the rest of the program.
Class:
public class MobileCharges { private double charges; private int minutes; private String plan;
class One { public static void doStuff() { System.out.println("One"); } }
class Two extends One
[code]....
My understanding of static says that static methods cannot be overrriden but the compilation of the above code results in Overriding rule violation error.
