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Classes

Brain Spout

Wizard No More
4,503
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#1
How do you simply state a class in java? im not sure how to explain what i mean so ill post the code and elaborate: (keep in mind that that ArrayList is properly imported and everything else to make the program work is good)

ArrayList d = new ArrayList();
d.add(new String("susanna"));

Object u = d.get(0);
String oohyeh = new String("ASSASASASAS");

if (u.getClass() == oohyeh.getClass())
{
System.out.println ("IN IF");
String ue = (String) u;
System.out.println (ue);
}

okay, i tried to instead of what i did say u.getClass() == String, whcih didn't work. I had no idea what to try from there so i tried == (class String). which ofcourse didnt work. im wondering if there is anyway to just have string there without having to declare the variable type i want to be compared to. im writing a program where different types of variables can be input in the same way, but slightly different things are done to each kind.

thanks
 

Brain Spout

Wizard No More
4,503
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#2
i thought someone here knew java. or is the question that hard and obscure. or is it impossible?

if anyone knows anything about this i got another question as well, related to this and about inheretance. it is:
i have a class rectangle, and then a class square that extends rectangle. if i make a square object and then set up the .getClass() on the square object and say == (Psudo Code - rectangle class) will it be true?
 

Smoke

Banned - What an Asshat!
2,583
0
0
#3
There are several people that know how to do it, I'm just not one of them, give it a little bit and then come back, i'm sure Jung, or someone else would help you with it.
 

Brain Spout

Wizard No More
4,503
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#4
im assuming that no one knows java, or no one knows the answer to this problem. either way with some experimentation i was able to find the answer to my problem. using the 'class' class:
http://java.sun.com/j2se/1.4.2/docs/api/java/lang/Class.html
there are several ways that one can have a class object to compare to another class object. the specific one i was looking for is forName(String name). a static method that returns the a class object. there are also a lot of other good methods that will help you if you are desinging your software without using a lot of premade code.
 

Jung

???
Premium
13,998
2,267
487
#5
Might want to ask BRiT, he's a Java developer. I'm admittedly horrible at java (mostly because I think it's a worthless language), and as such I avoid it. :D

Edit: I see you've answered your own question though.
 

BRiT

CRaZY
Founder
11,828
7,997
487
#6
Hey there, just saw this thread tonight, but it seems you found your own solution.

For something this simplistic use the following "instanceof" operator.


if (u instanceOf String) {
System.out.println("IN IF");
final String ue = (String)u;
System.out.println(ue);
}

Ideally, you could use the Class.isAssignableFrom method. This works for multiple levels of inheritence of interfaces and classes.

given "class A", "class B extends A", "class C extends B"

A objA = new A();
B objB = new B();
C objC = new C();

a.getClass().isAssignableFrom(c.getClass()); // TRUE
b.getClass().isAssignableFrom(c.getClass()); // TRUE
c.getClass().isAssignableFrom(c.getClass()); // TRUE
a.getClass().isAssignableFrom(b.getClass()); // FALSE
b.getClass().isAssignableFrom(c.getClass()); // FALSE


Oh, and btw, do not do the following: String a = new String("This is the string"); At compilation time, this creates 2 string objects as literals are converted into string objects by the compiler. The prefered and optimal means is simply: String a = "This is the String";


// The following creates 4 unique string objects in memory and is wasteful
String s1 = new String("A String");
String s2 = new String("A String");
String s3 = new String("A String");
String s4 = new String("A String");

// The following creates 1 unique string object in memory and has 4 pointers to it
String s1 = "A String";
String s2 = "A String";
String s3 = "A String";
String s4 = "A String";
 

Brain Spout

Wizard No More
4,503
111
177
#7
thankyou for the reply very insightful. when testing out how things work i like to make all my variables have seperate locations in memory because my program may run into a situation where two strings (or variables) that contain the same data have two different references. when testing i want to make sure i have taken that into account.