we're working with classes and interfaces and we see like this;
class class1 extends class2 implements interface1 { }. //it is valid
I want to know that why we cannot implement an interface before extending a class like this;
class class1 implements interface1 extends class2 { }. //it is invalid
Why java uses the keyword extends when setting the bound of a type parameter(Generic) to an interface. I think using the keyword implements is more intuitive.
public static <T extends Comparable<T>>
why use extends? and not implements.
int countGreaterThan(T[] anArray, T elem) {
int count = 0;
for (T e : anArray)
if (e.compareTo(elem) > 0)
++count;
return count;
}
I know if I want to set multiple bounds I will use extends keyword, and I will concatenate the bounds using & operator.
Is this a design decision to always use extends keyword to set bounds?
I'm reading about threads In Head First Java and the way an Instance of a class that Implements Runnable Is created confuses me a little.
public class MyRunnable implements Runnable ......
Runnable ThreadJob = new MyRunnable();
I thought I had to use this syntax :
MyRunnable ThreadJob =new MyRunnable();
How do you enforce any class which implements an interface should also implement comparable too? Say for instance you may have an interface
public interface Task
{ ... }
public class DoThis implements Task { ... }
public class DoThis1 implements Task { ... }
I want all of the classes which implements the interface Task to implement comparable too. Of course I can just say implements Task, Comparable. But is there something which we could do from interface level, i mean interface Task level?
I'll start off by showing my full code:
Main class
import javax.swing.JFrame;
public class groupingTest {
public static void main (String[] args) {
groupWindow test = new groupWindow();
[Code]....
At the start of the groupWindow it turns yellow and it says "The serializable class groupWindow does not declare a static final serialVersionUID field of type long".
I'm not sure why, but whenever I try to get a value out of a double, it only extends to one decimal place. For instance, (825 / 805) would become 1.0000 (after being run through a DecimalFormat object) instead of 1.0248 like I need it to be (and should be if what I know about primitive variable types is right). Why is the double variable type not giving me the precision I want and, more importantly, how do I fix this?
View Replies View RelatedI have two classes in two different files.
Color.java and Light.java
The Color class:
public class Color {
private int red;
private int green;
private int blue;
public Color(){
red = 0;
green = 0;
blue = 0;
}
And i have the Light class :
public class Light {
private Color color1;
private boolean switchedon;
public Light(int red, int green, int blue){
//dont know what to write here . how can i use the members of the Color class here ? without using extends.
}
}
I am trying to redefine the FileNotFoundException by creating a new class which extends it, but I am having difficulty. For my class practice, if no file is selected or passed in, an UnknownFileException should occur.My code is the following:
Java Code:
import java.io.FileNotFoundException;
public class UnknownFileException extends FileNotFoundException {
public UnknownFileException() {
super("We couldn't tell what file this is");
}
public UnknownFileException(String message) {
super(message);
[code]....
But I get a compile error stating an unreported FileNotFoundException.
I'm building a text editor. At this point, the editor should be able to read and write text and rich text. I create an instance of a RichTextEditor class that I created that extends a superclass I created (that extends JTextPane). Both my rich text and plain text classes extends the superclass I created. I use the this.read() to input my plain text from buffered reader. I think I need to use the read(fileinput stream, rtf document) method from type RTFEditorKit, but I cannot use that because it does not extend RTFEditorKit. I don't want to create a new class that extends RTFEditorKit because I need stuff from the JTextPane.
here are the classes on git... the super: TextEditorPane.java
The plaintext: TextEditorWrap.java
and the rich: RichTextEditor.java
I have fiddled with the read() method in different ways. In all cases, nothing loads. If I use the BufferedReader method, it doesn't give me an RTF, just the code for the RTF file.
How should I proceed? Do I create some sort of RTF interface and implement it?
I am working on a project where i need to show a year value in a class that extends JSpinner.Its working just fine but when i try to set an alignment value for the editor textfield it all falls apart and i know im missing something really critical here but i can't see or find it all i know is that i can't make a proper reference to the textfield component in the editor i use in the correct way or aproach.
public class JNumberSpinner extends JSpinner {
private String actionCommand;
private boolean isEnabled;
private int startValue;
private int columns;
private int alignment;
private SpinnerNumberModel model;
private JSpinner.NumberEditor numEditor;
private JFormattedTextField jTxtEditorView;
[code]....
a) I have a Ball Object which implements the Runnable interface and traces the various positions of a ball.
b) I then have a Ball_Bounce JPanel inside a JFrame which creates two instances of the Ball object and then paints them to the JPanel.
As per my understanding, when the main() program in Ball_Bounce.java is started, there a total of three threads running in this program, one for each ball and one for the main(). What I cannot understand is whenever the balls collide, I end up getting the "Collision" message twice even though the collision is checked only in the main() thread.
[#]public class Ball implements Runnable
{
private boolean xUp, yUp, xUp1, yUp1;
private int x, y, xDx, yDy;
private final int MAX_X = 500, MAX_Y = 500;
private boolean flag = true;
private static Thread ball;
[code]...
The assignment is to create a SmartString class that implements a SmartStringInterface class (created by professor) and implements a few methods. We are basically taking a string and then taking various substrings and inserting, deleting them and undoing changes as well. Here are the methods in the interface to use along with the parameters.
public interface SmartStringInterface {
public void insert(int pos, String sstring);
public void delete(int pos, int count);
public void undo();
public String toString();
The Undo is supposed to be able to be called multiple times (to be tested using a driver program that we must create) but the part that's got me is that the changes are only supposed to be stored. Currently, I am storing the "new" string after each change onto a stack, so that undo can just pop off the stack and it will revert to the previous string. Professor said that was wrong, so I don't know how to do it. Here is what I have so far (some of the code we have is using default StackADT stuff from our book, so if you need that I can post as well. You can see in the undo method where I currently save the string. We can use multiple stacks if needed, but the less the better. Must use at least 1. The exception code is already coded for us in another file also. I am only having to code these methods and the driver to test.
import java.util.Arrays;
public class ArrayStack<T> implements StackADT<T>
private final static int DEFAULT_CAPACITY = 100
private int top;
private T[] stack;
[code]...
Below code gets printed as output?
public interface I1 {
public void method();
}
public interface I2 {
public void method();
}
public interface I3 extends I2, I1 {
[Code] ....