Referring To Overridden Method From Supertype Reference?
May 14, 2015
If a method is overridden but you use a polymorphic (supertype) reference to refer to the subtype object with the overriding method, the compiler assumes you're calling the supertype version of the method.
is this true? maybe i'm misunderstanding it, but i thought the JVM looks at the object at run time and checks the object type. the context of the quote is about checked exceptions, but it seems like the statement should stand regardless of context. but this doesn't back up my experience. for example:
public class Test{
public void print(){
System.out.println("Super");
} public static void main(String[] args){
Test t = new SubTest();
[Code] ....
Will invoke the subclass method. like i said, maybe i'm missing something.
import java.lang.*; class InvalidValueException extends IllegalArgumentException {} class InvalidKeyException extends IllegalArgumentException {} class BaseClass { void foo() throws IllegalArgumentException { throw new IllegalArgumentException();
[Code] .....
Which one of the following options correctly describes the behavior of this program? And the answer is (definitely) --> The program will print : InvalidKeyException exception, but when i saw the explanation, it tells
It is not necessary to provide an Exception thrown by a method when the method is overriding a method defined with an exception (using the throws clause).
I don't know, but i think it will compiled because the Exception that is thrown by the foo method in DeriDeri class is inherited from unchecked exception.. so it is not necessary to declare throws statement on its method.. and if the exception was checked exception the answer must be different right?
Java Code: class A { int x=5; } class B extends A { int x=6; } public class CovariantTest { public A getObject() {
[Code] ....
And this is the output I get:
sub 5
I am unable to figure out how this is outputting 5 instead of 6. The getObject method of SubCovariantTest is obviously the one being called, and it returns a new B(). So why am I getting class A's x value? I thought since I was getting a B object returned that I would get B's x value.
TextButton up = new TextButton("up", textButtonStyle);
and .addListener is just one of the methods "TextButton" has (actually I think its inherited from "Button" but that doesn't matter).
Basically my question is what's going on inside the parentheses? From what I see its a new instance of "ClickListener" but then suddenly they override an actual method within. Is this simply just a way to override a method from the ClickListener class or is it something else?
I don't understand, why when in the constructor of the superclass A the method init() is called (line 4), the overridden version of the subclass is invoked (line 26) and not the superclass version (line 7):
class A { public A () { init(); } public void init() { System.out.println("test");
[Code] ....
I would have guessed that above code prints
test 1
But instead you get a NPE (because when the constructor of B is invoked
public static void main(String[] args) { new B(); }
Then there is first the implicit call to super:
public B() { s = " "; init(); }
Which is the constructor of A:
public A () { init(); }
But here now this init() method is not the version of A ( public void init() { System.out.println("test"); }) but the overriden version of the subclass (B): public void init() { System.out.println(s+=s.length()); }...
Which throws an NPE of course, because the initialization of s has not occured yet (it happens only after the implicit call to super() has finished (see public B() { s = " "; init(); }))
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 am trying to make a for loop using an iterator that refers to an object of a class that hasnt been made yet. The class is called MyArrayList but it does not have a Main. A MyArrayList object is made externally so I am unsure how to refer it to the object from within the class. Is there a place holder I could use such as Object.Iterator() or something similar. I have created an inner class that implements the Iterator interface. Here is the code that I need to adjust to do this:
public class ListIterator<E> implements Iterator<E> { public myIterator() { Iterator it = MyArrayList.iterator(); while (it.hasNext()) { System.out.println(it.next()); } } }
I 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!
I am trying to implement the following example to override the equality and hashCode method if the class has reference type member. I do get the expected result "true" for equal and "false" for non-equal objects. But the print statement in the Circle's equal method is not executed when the objects values are not equal. I don't know what i am missing, though i get the equality result "false" as expected for non equal objects.
class Point{ private int x, y; Point (int x, int y) { this.x =x; this.y = y;
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".
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 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?
I have an xml with 'n' number of data which i am parsing,for test i hardcoded without looping has below,now the below line is just parsing and showing the data for index '1' ,i need to loop this and i am not sure how can i do this.How do i find the length of obj and loop,i cannot find any method in SoapObject.I used like below but the data is getting overridden after parsing
for(int i=0;i<obj.getPropertyCount();i++) { KSoap2ResultParser.parseBusinessObject(obj.getProp erty(i).toString(), getReminder); } call in another class public static void parseBusinessObject(String input, Object output) throws NumberFormatException, IllegalArgumentException, IllegalAccessException, InstantiationException{
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); } }
Create an equals method that takes an object reference and returns true if the given object equals this object.
Hint: You'll need 'instanceof' and cast to a (Geocache)
So far I have:
public boolean equals(Object O){ if(O instanceof Geocache){ Geocache j=(Geocache) O; if (this.equals(j)) //I know this is wrong... but I can't figure it out return true; }
else return false; }
I think I have it correct up to the casting but I don't understand what I'm suppose to do with the this.equals(). Also I'm getting an error that I'm not returning a boolean... I get this all the time in other problems. I don't get why since I have to instances of returning booleans in this. "returns true if the given object equals this object" makes no sense to me. I assume the given object, in my case, is 'O'. What is 'this' object referring to?
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);
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.
I'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;
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.
