hello, I'm a beginner in Java and I use IntelliJ, and I'm looking to replace Class.forName() with something that uses more basic coding. My project structure is I created class Alpha, which contains only 1 variable (public static ArrayList<Beta>). Beta is another class I created, and it extends class Alpha. Beta contains many variables, the class type of one of them is something I created, let's call it Gamma. I also created a bunch of classes that extend Gamma, let's call one of them Delta. So Delta extends Gamma, which extends Beta, which extends Alpha. In the Alpha class, I have a public static method. Inside that method, I use scanner.next() to read a text file and save a letter to variable name, type String. Basically, that letter should refer to one of my Delta classes. So I used Class.forName(name) to fetch me the Delta class that has the same name as the letter (all my Delta classes have just 1 letter in the class name, each with different letter, so all my Delta subclasses are found under Gamma). Problem is this causes ClassNotFoundException. Can anyone please tell me how to fix it or what would be a simpler alternative to fetch a class with a String?
#How to get subclass from class name as String? (Class.forName not working)
north helm
hushed knollBOT
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visual hemlock
Use a Map<String, Class<?>> as a lookup table
Initialize it statically or in a constructor
trim saffron
hello, I'm a beginner in Java and I use IntelliJ, and I'm looking to replace Cla...
You have to use the fully qualified name, meaning including the package name
visual hemlock
Then all you do is get the class for a string, or throw an error
north helm
Use a Map<String, Class<?>> as a lookup table
like this? Gamma someVariable = Map<name,Gamma>;
north helm
Gamma g = (Gamma) map.get(name);
Ok, I initialized the map, but I don't understand why all the elements got saved as a Delta class that isn't even on the map lol I believe the scanner works properly because I have the right number of elements (using my test file), but they all got saved as Z which I added to the ArrayList once before the while loop, so only the 1st element should be Z. The capital letters are the Delta classes. I have below in my Alpha class.
public static ArrayList<Beta> listBeta = new ArrayList<>();
public static Map<String,Gamma> map = new HashMap<>()
{
{
Gamma c = new C();
Gamma d = new D();
Gamma e = new E();
Gamma n = new N();
put("C",c);
put("D",d);
put("E",e);
put("N",n);
}
};
public static ArrayList<Boolean> method (String filename) {
ArrayList<Boolean> result = new ArrayList<>();
listBeta.add(new Z());
Scanner scanner = null;
try {
File file = new File(filename);
scanner = new Scanner(file);
while (scanner.hasNext()) {
String s = scanner.next();
Gamma type = map.get(s);
listBeta.add(new Beta(type));
}
} catch (FileNotFoundException e) {
throw new RuntimeException(e);
} finally {
scanner.close();
}
[... I checked the elements' class types before this part of the code...]
return result;
}
I can't specify the package name, cause it needs to work on someone else's machine as well
trim saffron
I can't specify the package name, cause it needs to work on someone else's machi...
The package should not change across devices
north helm
The package should not change across devices
What should the line look like? I had something like this, where s is variable type String...
Class<? extends Gamma> type = Class.forName(s).asSubclass(Gamma.class);
trim saffron
What should the line look like? I had something like this, where s is variable t...
Seems correct
north helm
Seems correct
but that gave me the ClassNotFoundException, and I need the class for my method to do what it needs to do
trim saffron
Show me the code
/run
package a;
public class X {
public static void main(String[] args) throws ClassNotFoundException {
String s = "a.Z";
Class<? extends Y> type = Class.forName(s).asSubclass(Y.class);
System.out.println(type);
}
}
class Y extends X {}
class Z extends Y {}
turbid cargoBOT
Here is your java(15.0.2) output @trim saffron
class a.Z
Simple example⬆️
north helm
Show me the code
how do you get the package line to appear at the top? on my screen, I see a ton of imports... sorry, I'm really beginner...
trim saffron
Package (if there is one) should be above the imports
north helm
Package (if there is one) should be above the imports
/run
turbid cargoBOT
vestal krakenBOT
import java.io.File;
import java.io.FileNotFoundException;
import java.util.ArrayList;
import java.util.Scanner;
public class Alpha {
public static ArrayList<Beta> listBeta = new ArrayList<>();
public static ArrayList<Boolean> method (String filename) {
ArrayList<Boolean> result = new ArrayList<>();
listBeta.add(new Z());
Scanner scanner = null;
try {
File file = new File(filename);
scanner = new Scanner(file);
while (scanner.hasNext()) {
String s = scanner.next();
Class<? extends Gamma> type = Class.forName(s).asSubclass(Gamma.class);
listBeta.add(new Beta(type));
}
} catch (FileNotFoundException e) {
throw new RuntimeException(e);
} finally {
scanner.close();
}
for (int i = 0; i < listBeta.size(); i++) {
System.out.println(Gamma.getName(listBeta.get(i)));
}
return result;
}
public class Beta extends Alpha {
protected Gamma type;
protected boolean b1;
protected boolean b2;
public Beta() {
this.b1 = false;
this.b2 = false;
}
public <T> Beta (T type) {
this.type = (Gamma) type;
this.b1 = false;
this.b2 = false;
}
}
public class Gamma extends Beta {
static String name;
public Gamma() {
this.b1 = false;
this.b2 = false;
}
public static String getName(Beta beta) {
return name;
}
}
public class Z extends Gamma {
public Z() {
this.name = "Zero";
this.b1 = false;
this.b2 = false;
}
}
public class C extends Gamma {
public C() {
this.name = "Cookie";
}
} ```the rest of the Delta classes are pretty much as empty as C
trim saffron
What is the output?
If it is ClassNotFoundException then the string coming in from the file is incorrect
north helm
What is the output?
At this moment, the method should return an empty ArrayList<Boolean> but it does print to the console the list of names for each of the elements. The test file that I use is just a raw text file, the content looks like this: C E N D E
trim saffron
If it does print then what is the issue?
north helm
Ok, I think I figured out a simpler way to do this, but now I have a different problem lol so I will close this and open new post. Thank you everyone!
hushed knollBOT
Ok, I think I figured out a simpler way to do this, but now I have a different p...
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