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Type variable vs instanceof for identification


Type variable vs instanceof for identification

By : alexxxnf
Date : November 22 2020, 10:48 AM
hope this fix your issue Both are bad.
Define the method in A, override the method in X and Y and call that method on the object passed in. You're throwing away polymorphism, a cornerstone of object oriented programming.
code :
abstract class A {
    void doStuff();
}

class Y extends A {
    @Override
    void doStuff() {
        // Y specific implementation
    }
}

class X extends A {
    @Override
    void doStuff() {
        // X specific implementation
    }
}
void myfunction(A myobj) {
    myobj.doStuff();
}


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"illegal generic type of instanceof" when using instanceof on an inner class type?

"illegal generic type of instanceof" when using instanceof on an inner class type?


By : Werner Heinsohn
Date : March 29 2020, 07:55 AM
will help you Try ob instanceof Grafo.Par
I think that the compiler thinks that ob instanceof Par involves a runtime check on generic type parameters; i.e. that it is equivalent to ob instanceof Grafo.Par. But instanceof tests cannot check generic type parameters.
In Java, can I use a primitive type literal or type variable in an instanceof expression?

In Java, can I use a primitive type literal or type variable in an instanceof expression?


By : jimi pasa
Date : March 29 2020, 07:55 AM
I wish this helpful for you Nope, because of type erasure. An instance of MyClass doesn't actually know what T is.
You need to have an instance of Class. Then you can use the isInstance method. One way of doing that is to specify it in the constructor:
code :
class MyClass<T>
{
    private Class<T> clazz;

    MyClass(Class<T> clazz)
    {
        this.clazz = clazz;
    }

    // Now you can use clazz to check for instances, create new instances ect.
}
Object obj = 2;
boolean b2 = obj instanceof Integer;
instanceof operator is not working with Class type variable

instanceof operator is not working with Class type variable


By : Bareket Matmon
Date : March 29 2020, 07:55 AM
I hope this helps you . Yes, you should be using type.isInstance(a). instanceof is not for objects of type Class, but for class names, e.g. a instanceof String, not a instanceof String.class.
Use instanceof to check if some variable is class constructor type in typescript?

Use instanceof to check if some variable is class constructor type in typescript?


By : Lemon Tea
Date : March 29 2020, 07:55 AM
like below fixes the issue In Typescript, constructor functions are part of classes. The Typescript compiler will produce Javascript "constructor" functions (for ES5 or earlier) or for more recent versions of ECMAScript, the generated JavaScript will retain the class keyword.
The example below was inspired by the Typescript handbook section on instanceof type guards.
code :
interface Padder {
    getPaddingString(): string
}

class SpaceRepeatingPadder implements Padder {
    constructor(private numSpaces: number) { }
    getPaddingString() {
        return Array(this.numSpaces + 1).join(" ");
    }
}

class StringPadder implements Padder {
    constructor(private value: string) { }
    getPaddingString() {
        return this.value;
    }
}

function instantiateClass(myClass: new (...args: any[]) => any): Padder {
    if (myClass instanceof SpaceRepeatingPadder) {
        return new myClass(2 /* numSpaces */);
    } else if (myClass instanceof StringPadder) {
        return new myClass('*' /* value */);
    } else {
        return new myClass()
    }
}

let padder = instantiateClass(SpaceRepeatingPadder);
if (padder instanceof SpaceRepeatingPadder) {
    console.log("type narrowed to 'SpaceRepeatingPadder'")
}
if (padder instanceof StringPadder) {
    console.log("type narrowed to 'StringPadder'")
}

padder = instantiateClass(StringPadder);
if (padder instanceof SpaceRepeatingPadder) {
    console.log("type narrowed to 'SpaceRepeatingPadder'")
}
if (padder instanceof StringPadder) {
    console.log("type narrowed to 'StringPadder'")
}
type narrowed to 'SpaceRepeatingPadder'
type narrowed to 'StringPadder'
Why "t instanceof T" is not allowed where T is a type parameter and t is a variable?

Why "t instanceof T" is not allowed where T is a type parameter and t is a variable?


By : Matt Minix
Date : March 29 2020, 07:55 AM
fixed the issue. Will look into that further If you need T at runtime, you need to provide it at runtime. This is often done by passing the Class which T has to be.
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