The first is clear , new Person().printPerson(); displays Person but for the second : new Student().printPerson(); it accesses the Student constructor that points to the Person class => object. It builds the Person instance then goes back to the Student constuctor .Both methods are private and to my knowledge invisible one to the other , except that you cant run the the Person one because it's private so the only one in the Student class is the Student one . Guess it 's incorrect , but why ? (is because private methods cant be overriden and somehow the super class one always has priority ? , even if it's private?)
public class Test {
public static void main(String[] args) {
new Person().printPerson();
new Student().printPerson();
So I'm just a little unclear about this, but how would I call methods from the 'top' of an inheritance chain? I say 'top' because Object is the top... E.g.:
public class AClass { public void myMethod() { ... } } public class BClass extends AClass { public void myMethod() { ... } } public class CClass extends AClass { public void myMethod() { ... } }
Assuming that BClass.myMethod() completely overrides AClass.myMethod() (so that there is no call to super.myMethod() in BClass.myMethod()) How can I call AClass.myMethod() from CClass.myMethod()?
I've an interface with generic methods in it. I would like to have specialized methods in the sub types. While doing that I'm seeing the following warnings in eclipse.
class Sorter { <E> void sort(E[] elements); };
class StringSorter {
// This gives me a warning 'hiding' to 'sort' <String> void sort(String[] elements) { }
// Gives me an error "The method someCrap(String[]) in the type StringSorter is not applicable for the arguments (String[])" void someCrap(String[] elements) { } };
I would like to understand why eclipse gives the above warnings and errors.
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;
I thought you can only create a new object using private implementations and then using a constructor to set your arguments inside the parameters of the constructor to the instance variables but how come he created an object without any private implementations and just methods inside the constructor.
import javax.swing.JFrame; public class MyWindow extends JFrame { public static void main(String[]args){ new MyWindow(); } public MyWindow(){ setSize(500,500); setVisible(true); setTitle("MyWindow"); } }
If i have a class(lets say class name is Approval) with the following private members: String recip_id, Int accStat, String pDesc, String startDate How can i create public get and setter methods for these private members of the class?
So I'd like to know what all the statement, not sure if it's the correct way of calling them but I'd like to know what like all of those purple-ish colored words in eclipse actually mean.Here's what I know so far, so if you can add some stuff to it or just correct me:
public - can be accessed by different classes. private - can't be accessed by different classes. static - adds a '.' which pretty much lets you like use methods on it? Not really sure about this one. final - a final value of a variable meaning it couldn't and willn't change? super - I have no clue, maybe something that has to be executed first? Not sure. void - bassicly you don't have to use return as it doesn't return any value. this - Uh-.. I think it has something to do with the class this keyword has been entered into, not quite sure what it does though.
I assume there are alot more but I am just not sure about these common ones, what the actually do and what's their purpose?
I'm learning about inheritance and part of my problem is to create an Order with methods, then an UpdateOrder where the total price is changed by adding four dollars to it, and then a main method displaying a few orders. I've copied all three below in order. My question is when I run the program it will display the totalprice() first for the second order followed by name, number, etc.what you override always displayed first regardless of the order you put them in? (The issue is at line 31 on the third code.)
import javax.swing.JOptionPane; public class Order { //superclass private String customerName; private int customerNumber; protected int quantityOrdered; protected double unitPrice; protected double totalPrice;
I am new to java i dont understand the difference between the abstract and inheritance i mean we use the abstract class with extends with other class name ,even we do that same in the inheritance pls tell me main difference between abstract and inheritance...
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 am in an intro programming class and we got assigned a problem for creating a super class with about a dozen sub classes for generating a random word(via WordGetter class) and then comparing that word to a variety of different patterns(like: does the word contain "re"). We were given the super class which looks like this...
public class Pattern { public boolean matches(String text) { return true; } public String toString() { return "(TRUE)";
[code]...
and from this class, we have to write subclasses that override those three methods. I am struggling to understand inheritance and I am not really sure where to even start. Here is the instructions for the first sub class we need to write...
"CONTAINS" SUBCLASS Constructor: The constructor accepts a String named ‘letters’.
Matches: This pattern matches any text that contains at least one occurrence of each ‘letter’. toString: produces the text “(CONTAINS <LETTERS>)” where <LETTERS> is the ‘letters’ string. getLetters(): this method must return letters. equals(Object): careful on this one. Two Contains are equal if they have the same letters (order is not relevant). (Example):
Pattern p = new Contains(“re”); boolean f1 = p.matches(“renew”); // f1 is true boolean f2 = p.matches(“zoo”); // f2 is false String s = p.toString(); // s is “(CONTAINS re)” boolean f3 = p.equals(new Contains(“er”)); // f3 is true.. really..
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?
public abstract class Boat{ private int height; private int length; private int width; private double boatValue; private double chargeRate; private Owner owner; public Owner getOwner() { return owner;
i was leaning inheritance and tried to implement it in Java.This is my base class vehicl.java
public class vehicle{ private int topSpeed; private int cubicCap; private String modelName; private boolean hasAlloy;
[code]...
I also have a derived class called car.java.What i wanted to do in the derived class was that i wanted to override the constructor as well as the getInfo() method from the base class.I wanted to add an additional attribute to the car "numberSeats" and display tat too when the object to car class calls the getInfo() method .It showed an error "identifier required" when i tried to compile car.java program.
import java.util.Scanner; public class car extends vehicle{ //int numberSeats; //System.out.println("Enter the number of Seats"); Scanner numberSeats=new Scanner(System.in); numberSeats=numberSeats.nextInt(); //System.out.println(numberSeats.nextInt());
[code]....
explain the errors that i get when i tried to compile car.java without using super keyword or without defining the constructor from the Car class ?
I am creating a slot machine using eclipse. I am trying to get the "winnings" JTextField to be updated in a way so that when the random images have been selected it adds to the number that is already displayed in the JTextField as opposed to what it is doing at the minute which is just displaying how much was won on that particular spin. I am also struggling to set a code for when noting is won, nothing is added. My code is below.
I'm working on a project that contains multiple classes. Each class contains and must contain only PRIVATE variables. Here's my issue. When my test code calls for a new instance of "StudentClass" as so:
StudentClass studentClass = new StudentClass(offeredClass.getClassIdNumber(), offeredClass.getClassName(), offeredClass.getClassroom());
The corresponding constructor won't let me initialize it's variables because they are declared private within another class, as shown here:
When getClassName, getClassroom, and getClassIdNumber are passed to a toString() method elsewhere in my test code. the output is returned just fine. When passed through the StudentClass, I'm getting Null across the board.
public class StudentNumber { /* public StudentNumber(){ System.out.println("test"); } */ private char c='W'; public StudentNumber(float i){ System.out.println(i);
[Code] ....
Exception in thread "main" java.lang.RuntimeException: Uncompilable source code - c has private access in extention.pkgsuper.StudentNumber at extention.pkgsuper.ExtentionSuper.main
I am writing small pieces of code to make sure I understand Java basics and I have the following.
package teams1; public abstract class Team1{ private String sport = new String(); public abstract String getSport(); public abstract void setSport(); } import teams1.*;
[Code] .....
It doesn't compile because sport is private in the super class, but I thought FootballTeam1 would inherit it's own copy of sport because it is extending Team1.
I have a working program, except that it does not calculate the credit hours and the financial aid. When I enter an input, it works, until it should show the student name, credit hours and financial aid. the error i get from the command is "Hours invalid for false student". Here is the program i think i might have the problem.
import java.text.DecimalFormat; public abstract class Student { //initialise variables String name; int creditHrs;
