This is my class structure.
public class Node<T> {
private T value;
public Node(T val) {
this.value = val;
}
public T evaluate() {
return value;
};
}
T can be Integer, Double, Date, Long or String.
Now, is there anyway I can get to know exactly what that type T is? Thanks.
You can invoke getClass() method on that generic variable and find out the class. Basically generics are erased at run-time, so an unbounded generic is nothing but java.lang.Object. So you can invoke all the method supported by Object class on that generic variable
At run-time, getClass() on generic object will return the actual class which was used to substitute the generic
For example
public class Node<T> {
private T value;
public Node(T val) {
Class<?> clazz = val.getClass();
checkType(clazz);
this.value = val;
}
public T evaluate() {
return value;
};
private void checkType(Class<?> c) {
if(c.getName().equals(Integer.class.getName())) {
//...
}
}
}
Integer as type parameter class, but it was actually instantiated as Node<Number>.Much easier, use instanceof.
public class Node<T> {
private T value;
public Node(T val) {
checkType(val);
this.value = val;
}
public T evaluate() {
return value;
};
private void checkType(T val) {
if(val instanceof Integer) {
//...
}
}
}
Though there is already an accepted answer, I think it may be good to add one more answer:
As mentioned by @BaileyS, there is no way to get info of T in a place without an instance of T.
The solution greatly depends on why you want T, how you are using it. Normally, if we need the type of T for the logic (e.g. creating a new instance of T), it is usually done by providing the Class instance.
For example, you can make your Node class be:
public class Node<T> {
private T value;
private Class<T> valueType;
public Node(T val, Class<T> valueType) {
this.value = val;
this.valueType = valueType;
}
//.....
}
If you know that your node will store only Number you could restrict it.
public class Node<T extends Number> {
private final T value;
public Node(T val) {
this.value = val;
}
public T evaluate() {
return value;
};
public Class<? extends Number> type() {
return value.getClass();
}
}
