#How can I compare Type Parameter T2 with T?

47 messages · Page 1 of 1 (latest)

quartz lotus
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I'm trying to compare this-quantity (T) with another quantity (T2), can someone give me a hint how to solve this?

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ionic galleonBOT
#

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glad moss
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T1 and T2 are different types, so they should never be equals anyways. This breaks all laws.

glad moss
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I mean they CAN be the same type, but if you're comparing them then they SHOULD be the same type.

#

You can check if they are derrived from the same class and then cast them accordingly if you want

ionic galleonBOT
#

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worn moss
#

sure you don't want public Intervall<T> schnitt(Intervall<T> anderes) for the intersection?

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that would enforce both being the same type

quartz lotus
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This is the method signature which my professor gave me: public <T2> Intervall<T> schnitt(Intervall<T2> anderes) and I should think of an bound for T2 with which I can solve the task: form an intersection of this and anderes. And I thought about comparing the this-intervall with anderes-Intervall to check if this is within anderes

quartz lotus
worn moss
quartz lotus
worn moss
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no

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you need to provide some way of comparing them to each other

#

if you have a common superclass that is comparable, you could just use intervals of that

quartz lotus
#

Ok I’m going to try that I thought I already tried using lower bounds

quartz lotus
#

from my understanding firstly T2 needs to extend comparable, so it is comparable at all. Also T2 has to be a superclass of T in order to make sure that T is comparable with T2

worn moss
#

Can you show the whole class as text?

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not as an image

quartz lotus
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public class Intervall<T extends Comparable<T>> {
    private T untereGrenze;
    private T obereGrenze;


    public Intervall(T untereGrenze, T obereGrenze) {
        this.untereGrenze = untereGrenze;
        this.obereGrenze = obereGrenze;
    }

    public boolean isLeer() {
        return untereGrenze == null || obereGrenze == null
                || obereGrenze.compareTo(untereGrenze) < 0 || untereGrenze.compareTo(obereGrenze) > 0;
    }

    public <T1 extends Comparable<? super T>> boolean enthaelt(T1 wert) {
        return (wert.compareTo(untereGrenze) > 0 && wert.compareTo(obereGrenze) < 0
                || wert.compareTo(untereGrenze) == 0 && wert.compareTo(obereGrenze) == 0
                || wert.compareTo(untereGrenze) == 0 && wert.compareTo(obereGrenze) < 0
                || wert.compareTo(obereGrenze) == 0 && wert.compareTo(untereGrenze) > 0);
    }

    

    public <T2 extends Comparable<? super T>> Intervall<T> schnitt(Intervall<T2> anderes) {

        return null;
    }
}
worn moss
#

public <T2 extends Intervall<? super T>> Intervall<T> schnitt(T2 anderes){ should work

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the issue is that you can't have Intervall<T2> as that would require T2 to extend Comparable<T2>

quartz lotus
#

my professor gave me this method signature: ```java
public <T2> Intervall<T> schnitt(Intervall<T2> anderes)

Think carefully about the bounds for T, T1, and T2 so that the following task is solvable! So i cant change the paramterlist nor the method signature only the bounds
worn moss
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public <T2 extends Comparable<T2>> Intervall<T> schnitt(Intervall<T2> anderes) { would be possible but that wouldn't allow comparing T1 and T2

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public <T2 extends Comparable<? extends T>> Intervall<T> schnitt(Intervall<? extends T2> anderes) { maybe?

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my fault, should be public <T2 extends Comparable<? super T>> Intervall<T> schnitt(Intervall<? extends T2> anderes) { I think

quartz lotus
#

sadly this doesnt work either, maybe my approach with comparing the values is wrong? I really tried everything I could think of to make this work

worn moss
#

that compiles for me

public class Intervall<T extends Comparable<T>> {
    private T untereGrenze;
    private T obereGrenze;


    public Intervall(T untereGrenze, T obereGrenze) {
        this.untereGrenze = untereGrenze;
        this.obereGrenze = obereGrenze;
    }

    public boolean isLeer() {
        return untereGrenze == null || obereGrenze == null
                || obereGrenze.compareTo(untereGrenze) < 0 || untereGrenze.compareTo(obereGrenze) > 0;
    }

    public <T1 extends Comparable<? super T>> boolean enthaelt(T1 wert) {
        return (wert.compareTo(untereGrenze) > 0 && wert.compareTo(obereGrenze) < 0
                || wert.compareTo(untereGrenze) == 0 && wert.compareTo(obereGrenze) == 0
                || wert.compareTo(untereGrenze) == 0 && wert.compareTo(obereGrenze) < 0
                || wert.compareTo(obereGrenze) == 0 && wert.compareTo(untereGrenze) > 0);
    }

    

    public <T2 extends Comparable<? super T>> Intervall<T> schnitt(Intervall<? extends T2> anderes) {
          anderes.untereGrenze.compareTo(untereGrenze);
        return null;
    }
}
quartz lotus
#

it says "Provided:
capture of ? extends T2" "Required type:
T"

worn moss
#

you mean where you call it?

quartz lotus
#

omg wait I compared it the other way around like this: this.untereGrenze.compareTo(anderes.obereGrenze);

#

I think u got it right, it works now. Im writing the method now and test if it works, thank you vm for your help

ionic galleonBOT
worn moss
#

and maybe you need to change the class declaration to public class Intervall<T extends Comparable<? super T>>

quartz lotus
#

so for me to understand it: what we did is: T2 extends Comparable<? super T>> meaning, T2 has to be comparable and must be a Superclass of T. (Intervall <? extends T2> anderes) the paramter anderes must be from type Intervall and a Subclass of T2?

quartz lotus
worn moss
ionic galleonBOT
worn moss
# 
public class Intervall<T extends Comparable<? super T>> {
    private T untereGrenze;
    private T obereGrenze;


    public Intervall(T untereGrenze, T obereGrenze) {
        this.untereGrenze = untereGrenze;
        this.obereGrenze = obereGrenze;
    }

   
    public <T2 extends Comparable<? super T>> Intervall<T> schnitt(Intervall<? extends T2> anderes) {
          anderes.untereGrenze.compareTo(untereGrenze);
        return null;
    }
}

import java.time.*;
import java.time.chrono.*;

Intervall<LocalDate> a = new Intervall<>(LocalDate.now(), LocalDate.now());
Intervall<ThaiBuddhistDate> b = new Intervall<>(ThaiBuddhistDate.now(), ThaiBuddhistDate.now());
a.schnitt(b);

seems to work for me

quartz lotus
#

Yes it has to work, it makes all sense, thank you again! T

ionic galleonBOT
quartz lotus
#

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