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Java generics work by checking types at compile time and inserting appropriate casts, but erasing the types in the compiled files. This makes generic libraries usable by code which doesn't understand generics (which was a deliberate design decision) but which means you can't normally find out what the type is at run time.
May 24, 2016 · The signatures would become: public <T extends Animal> void addFriend(String name, Class<T> type, T animal); public <T extends Animal> T callFriend(String name, Class<T> type); Inside both methods you should check that the parameters are sane. See Effective Java and the Class javadoc for more info.
Now, if Java had generics from the beginning and didn't have types, such as LinkedList, that were originally created before it had generics, it probably could have made it so that the constructor for a generic type automatically infers its type parameters from the left-hand side of the assignment if possible. But it didn't, and it must treat raw types and generic types differently for backwards compatibility.
Oct 19, 2011 · The simplest way I can think of to explain generics is the good ol' copy-paste metaphore: public <COPY> PASTE addTwoThings(PASTE a, PASTE b) {. return a + b; } You specify a type (in the <COPY> portion) and java use this type throughout the code block, and it will make sure that the types are compatible. By doing it this way, you avoid having ...
Jan 25, 2017 · As the other posts have noted, you are asking about a Java feature called generics. In C++, this is called templates. This feature in Java is usually easier to work with than the that found in C++. Let me answer your questions functionally (if that's not a naughty word for OO discussions). Before generics, there were concrete classes like Vector.
Dec 27, 2013 · This allows you to use the compareTo method for comparing items in the tree. In the GBinTree class, the add method uses item.compareTo(bn.item) instead of the < operator for comparison. This ensures that the comparison is done using the compareTo method of the generic type T. The toString method in the GBinTree class now checks for root == null ...
Dec 27, 2019 · package generics.basics; import java.util.ArrayList; import java.util.List; public class GenericMethods { /* Declare the generic type parameter T in this method. After the qualifiers public and static, you put <T> and then followed it by return type, method name, and its parameters.
Sep 17, 2008 · 25. If you need a new instance of a type argument inside a generic class then make your constructors demand its class... private Class<T> typeArgumentClass; public Foo(Class<T> typeArgumentClass) {. this.typeArgumentClass = typeArgumentClass; public void doSomethingThatRequiresNewT() throws Exception {.
Aug 30, 2008 · While, C++ is platform dependent language, Java is platform independent language. The above statement is the reason why C++ is able to provide true generic types. While Java does have strict checking and hence they don't allow using generics the way C++ allows it. answered Jul 12, 2020 at 15:19.
Jul 24, 2012 · In very extreme cases (pre-Java 7 without AutoCloseable), I would have liked to be able to do that, too. E.g. <E extends Connection or Statement or ResultSet> That would've allowed me to call E.close() , no matter what the actual type was.
