why interfaces are needed in Java,Now you saw what a class must do to avail itself of the s... - justpaste.it (if I paste the quote here, I get the "Page not found" error after posting -.^)
the first fragment reads that the compiler must be sure that a method exits at a compile time, whereas the second fragment denies it - if a[i] doesn't have the specified compareTo method, a JVM simply throws an exception.
Let's say I'd like to print out something as a prompt without end with a new line char, so the standard System.out.println() is not an option and I'd like to find something else inplace of println().
Where to find that? I googled about that and learned printf() is the one I want, but how to get it from java api documentation.
I understand that interface methods are abstract. I don't understand what the methods in the API do if the method bodies are empty. For example, say there are two interfaces, both with one method with no parameters. What would make these two interfaces different from each other. In the API, the AudioClip interface has the methods play(), stop(), and loop(). If abstract methods have no method bodies, and these methods take no parameters, what makes them different from each other.
View Replies View RelatedWhy can't we have static methods in an interface?
View Replies View RelatedThis is my assignment.
Identify how multiple inheritance is possible in Java with interfaces.
Write a java programme with appropriate classes to demonstrate the above.
Hint: both inheritance and interface concepts are necessary.
For the project name in netbeans, use your id and the name "assignment" separated by underscore,
E.g. 9876543_assignment
how can i implement multiple inheritance in java using interfaces. if interfaces have some methods having same name then how to distinguish that ?
View Replies View Relatedmethod called []getLetterGrades but the only hint My professor told me was that I needed to declare another array list for this method and he wouldnt tell me anything else so bummer. But I don't understand why if what we are returning is a char. It would make sense to return an array list of char to get letter grade. Which is what i did but since the function is a char, the array list character wont work as a return.Primarily i would like to know the type that is needed. I just want an explanation for an array list in this method and how it would serve in this method.
import java.io.File;
import java.util.ArrayList;
import java.util.InputMismatchException;
import java.util.Scanner;
[code]....
Should we always use getters/setters, e.g. even in something like
Java Code:
class Foo {
private static int foo;
public int getFoo() {
return foo;
}
public void setFoo(int fig) {
foo = fig;
}
} mh_sh_highlight_all('java');
Or should we use the only when there is a good reason to use them, e.g. validation for a setter or may be computing a value to return from some variables etc. ?
I have a HTML page with an applet inside it.I have the applet class and all other needed classes in a jar file in jre/lib/ext folder (I'm on windows). But when I open the HTML file in a browser it gives me ClassNotFound exception..The HTML file is this:
<HTML>
<HEAD>
<META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=windows-1252">
<TITLE>
DPI 3270 Printer Session
</TITLE>
</HEAD>
<BODY topmargin="0" leftmargin="0">
<SCRIPT SRC="HODVersion.js" LANGUAGE="JAVASCRIPT"></SCRIPT>
<P>
[code]....
I have this HostOnDemand class in its package in a jar file in jre/lib/ext but it can't be found.Since the applet is way too old, I'm using jre1.4.2 and netscape.
I have a .jar that is installed in other computer(outside netbeans). Everything works fine except with report. I am sure the libraries needed for iReport is added in my lib folder but I receive this error message when I to load the report using the program.I use command prompt to see the error:
Java Code:
java -jar projCosting.jar mh_sh_highlight_all('java');
And here is the error message:
Java Code: net.sf.jasperreports.engine.JRException: Error compiling report java
source files : [b]D:CostingRptCosting_1288072391310_955208.java[/b]
at net.sf.jasperreports.engine.design.JRJavacCompiler.compileClasses
[code]....
I have included the library in lib folder but do you think I have to install the iReport application?
The keys in a HashMap and the values in a Set must all be unique, but this can be circumvented when using custom objects in a HashMap and Set, because the compiler has no way to determine if the objects are equal or not, as shown in the example below:
Java Code:
import java.util.LinkedHashMap;
import java.util.Map;
public class HashCodeEquals {
public void run(){
Person p1 = new Person(1, "John");
Person p2 = new Person(2, "Matt");
Person p3 = new Person(1, "John");
[code]....
Obviously the equals method is needed because that compares the two objects. But why is the hashCode method needed?
I have a simple classes here one is interface and another one is abstract class when i try to compile them abstract class is givving compilation error.
public interface MyInterface{
public void getName();
public void getName(String s);
}
public class HelloWorld{}
abstract class SampleClass{
[code]....
I have to meet certain requirements for this one program, and one of them is as follow: The program will require the user to enter the needed values one after another. If any of the entered values is invalid, then the program will detect that and go into a loop requiring the user to enter a valid value. The program must keep track of the total number of invalid values that the user has entered.
I know how to set a restriction and create a loop to keep asking the same question until it is satisfactory ( in this case I used a while loop) but I am at loss on how I should keep track of the total number of invalid values. I know I can use an increment but how do I set a variable for when the program meets an wrong input from the user.
Interfaces are 100 % abstract classes.They cannot be instantiated.Their sole purpose is to be implemented.So why does the following code works just fine while it is attempting to instantiate an interface.
interface TestA { String toString(); }
public class Test {
public static void main(String[] args) {
System.out.println(new TestA() {
public String toString() { return "test"; }});
}
}
Can i use constructors in an interface?
interface AI {
public abstract AI();
public abstract void hello();
}
Output:
I got the error as the method AI() should have return type.
This is the link [URL] and it says One significant difference between classes and interfaces is that classes can have fields whereas interfaces cannot.How can this be possible?
View Replies View RelatedIn Interview many times Interviewer ask a simple question "Hibernate core Interfaces ?".The five core interfaces exposed by Hibernate. But he not satisfy, Why?...
View Replies View Related I did research again....
interface:
methods - abstract, default, static ONLY(abstract methods have no body, while static and defaults do, right?)
fields - public, static, final ONLY
abstract class: a normal class, but has at least one abstract method
methods - all
i.e., static, non-static, abstract (can it have a default method?)
fields - all
i.e., public, protected, private / final, non-final / static, non-static
When are we allowed to nest interfaces inside a class? Would this be possible? Why or Why not?
View Replies View RelatedI have three classes of object, most of which must implement two out of three interfaces. The interfaces look like this:
public interface Source {
public void startSending();
} public interface Sender {
public void setReceiver();
[Code] .....
That works fine, but I am wondering if pairing the interfaces into subinterfaces is a defensible methodology. For example, all classes that act like Producer must implement both the Source and Sender interfaces. And all classes that act like Relayer must implement the Sender and BlackHole interfaces. I could define two subinterfaces like this:
public interface Factory extends Source, Sender {
}
public interface Modifier extends BlackHole, Sender {
}
I could then define my classes like this:
public class Producer implements Factory {
}
public class Relayer implements Modifier {
}
public class Consumer implements BlackHole {
}
Within the class definitions, it makes no difference, as I will have to implement the same methods either way. But it seems more self-documentary to create the subinterfaces from their parent interfaces and name them in ways that reflect what the classes that implement them must actually do.
I am trying to figure out how I can most easily make it easier to make new types of units in my game. I have buildings and ships, and would like to know how I could make it easy to add new units. I have been recently told about interfaces, and have worked with inheritance a little bit.
What I would like to able to do is have it so that all of the variables and methods common to all ships could be stored in a superclass or interface, and same with the buildings. I would also like to be able to assign behaviours to the buildings and ships, maybe as interfaces, which could contain all of the methods and variables required for the functions of that ship or building.
For example, creating a new type of building that can shoot, build ships, and can regenerate nearby ships. So it would possible inherit all of the variables and methods common to all buildings, such as health, image, x, y, getX(), getY() etc. But it would then also gain the variables and methods essential for its functionality, such as shootRange, shoot(), regenRate, etc.
How could this best be achieved?
I am reading about interface and i see that classes are allowed inside interfaces which are implicitly static. Here is sample of code i created and i am able to access the static method and fields as well. Here is the code snippet.
public class TestInnerClass {
public static void main(String[] args){
Test.NestedClass.printMe();
}
}
interface Test{
static class NestedClass{
static int x = 100 ;
public static void printMe(){
System.out.println(x);
}
}
}
My question is what is the use of such static classes inside interface? If i don't have access to Foo, i can't ever invoke NestedClass. Whats the design usage?
I want to make some library interfaces for a graph.Using these interfaces:
Graph<V,E>
Edge<E>
Vertex<V>
how can i constraint users of this library to use the same type <E> in the graph and edge interface and type <V> in the graph and vertex interface??
While reading the design patter book, i got one doubt ,There is a List an interface having sub classes ArrayList, LinkedList etc.,
Q1) My question is Why they declared the List as interface rather than Abstract class?
Q2) i read some site -
List l = new ArrayList(); Why it is GOOD line?
ArrayList l = new ArrayList() ; Why it is BAD line?
Answer required with detailed information for Q1 and Q2.
import java.util.*;
public class CommonElements
{
private int comparisons; // number of comparisons made
private Comparable[] arrayToSearch; // current array being traversed
private Comparable[] commonElements = new Comparable[10];
private int arrayPosition = 0; //keeps track of what index to add an element to common at
[Code] ...
I have trying to get this down to the bar minimum. I am trying to cast the desired object array to a array of comparable. This is all required by the assignment.
I am getting a runtime error that I can not perform the desired cast. What do I need to provide the compiler in order to allow for this casting. I can not change the signature of the method however nothing about the class has been specified do I need to implement comparable? Also I don not now what the client is passing so how would I write a generic compareTo method to compare object of unknown types.
imagine you are implementing 2 interfaces having identical method signatures:
interface A {
void doStuff();
}
interface B {
void doStuff();
[Code] ....
How can I implement both methods?
Or another example with member variables:
interface A {
public static final int i = 3;
}
interface B {
public static final int i = 33;
[Code] ....
How can I go about making clear which 'i' is meant?