Minato Namikaze :
I am playing with Java utility functions. I have the following code:
public class Checker<T>{
private T value;
private Function<T, T> callback;
private Checker(T value) {
this.value = value;
}
public static Checker when(String o) {
return new Checker<String>(o);
}
public static Checker when(int o) {
return new Checker<Integer>(o);
}
public Checker then(Function<T, T> callback) {
this.callback = callback;
return this;
}
public void execute() {
if (this.value instanceof String) {
this.callback.apply("123");
}
if (this.value instanceof Integer) {
this.callback.apply(123);
}
}
Checker.when("123").then(str -> {
return "";
}).execute();
Checker.when(123).then(str -> {
return "";
}).execute();
Now here I am getting an error for this.callback.apply("123") as it requires T and cannot cast it to String.
Is it possible to have generic return types for Function<T,T>? I can send T, but then its received as an Object in my lambda, but I want as String or Integer.
Eran :
I made some changes in your Checker class which make sense to me. I eliminated all the raw types, and I used the value member in execute. I added a return type of execute, in order to be able to print its result.
class Checker<T>{
private T value;
private Function<T, T> callback;
private Checker(T value) {
this.value = value;
}
public static Checker<String> when(String o) {
return new Checker<>(o);
}
public static Checker<Integer> when(int o) {
return new Checker<>(o);
}
public Checker<T> then(Function<T, T> callback) {
this.callback = callback;
return this;
}
public T execute() {
return this.callback.apply(value);
}
public static void main (String[] args) {
Checker.when("123").then(str -> {
return "." + str + ".";
}).execute();
Checker.when(123).then(i -> {
return i + 100;
}).execute();
}
}
Now when you check your class with:
System.out.println (Checker.when("123").then(str -> "." + str + ".").execute());
System.out.println (Checker.when(123).then(i -> i + 100).execute());
You get:
.123.
223
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