overriding

问题 I extend a TreeMap, override "put()", and do something equivalent to: public class MyMap<K, Integer> extends TreeMap<K, Integer> { @Override public Integer put(K key, Integer value) throws ClassCastException, NullPointerException { java.lang.Integer newValue = java.lang.Integer.valueOf(123); super.put(key, newValue); // <--- error message here return newValue; } } error message: no suitable method found for put(K, java.lang.Integer)... java.lang.Integer cannot be converted Integer. I know it

问题 I'm overriding a property in my derived class that I would like to make it readonly. The C# compiler won't let me change the access modifiers, so it must stay public. What's the best way to do this? Should I just throw an InvalidOperationException in set { } ? 回答1: Having the setter throw an InvalidOperationException in a derived class violates the Liskov Subsitution Principle. Essentially makes the usage of the setter contextual to the type of the base class which essentially eliminates the

问题 Abstract member method is illegal in a singleton object scala> object Foo { | def g: Int | } def g: Int ^ On line 2: error: only traits and abstract classes can have declared but undefined members as is abstract value member scala> object Foo { | val x: Int | } val x: Int ^ On line 2: error: only traits and abstract classes can have declared but undefined members however abstract type member is legal in a singleton object scala> object Foo { | type A | } object Foo so clearly the sense in

问题 Abstract member method is illegal in a singleton object scala> object Foo { | def g: Int | } def g: Int ^ On line 2: error: only traits and abstract classes can have declared but undefined members as is abstract value member scala> object Foo { | val x: Int | } val x: Int ^ On line 2: error: only traits and abstract classes can have declared but undefined members however abstract type member is legal in a singleton object scala> object Foo { | type A | } object Foo so clearly the sense in

问题 So, I'm trying to figure out the best (most elegant with the least amount of code) way to allow overriding specific functions of a property (e.g., just the getter, just the setter, etc.) in python. I'm a fan of the following way of doing properties, due to the fact that all of their methods are encapsulated in the same indented block of code (it's easier to see where the functions dealing with one property stop and the functions dealing with the next begin): @apply def foo(): """A foobar"""

问题 I'm using unity, and unity does not have a tuple in it, so I created my own tuple class to work since I needed it for my Dictionary. Dictionary <Tuple<int,int>, Tile> Tile class that I created and isn't really relevant to solve this problem(at least I think it wont help). But the problem is that I'm using both negative and positive integer in my tuples, and when I use my current GetHashCode() with the Tuples , sometimes I get the same HashCode, for example Tuple<-10, 8> and Tuple<-9,-10> both

问题 When I was reading Thinking in Java (4th Edition) recently, I got a problem about method binding in Java. First let's look at two definitions from the book: Connecting a method call to a method body is called binding. All method binding in Java uses late binding unless the method is static or final. you can find those definitions in section Method-call binding from chapter Polymorphism . (page 281-282) To testify that, I wrote the following code: public class Test3{ public static void main

问题 When I was reading Thinking in Java (4th Edition) recently, I got a problem about method binding in Java. First let's look at two definitions from the book: Connecting a method call to a method body is called binding. All method binding in Java uses late binding unless the method is static or final. you can find those definitions in section Method-call binding from chapter Polymorphism . (page 281-282) To testify that, I wrote the following code: public class Test3{ public static void main

问题 I use this line of code in an app with XCode 10 in order to dim the home indicator on iPhone X and associated edgeless apple devices. override func prefersHomeIndicatorAutoHidden() -> Bool { return true } Now the funny thing is, I have an exact copy of this app and on one copy the code works, whilst on the over the code does not compile: Method does not override any method from its superclass Indeed when I start typing "prefers..." , prefersHomeIndicatorAutoHidden appears as a read-only

问题 I have four classes. Request, DerivedRequest, Handler, DerivedHandler. The Handler class has a property with the following declaration: public abstract Request request { get; set; } The DerivedHandler needs to override this property so that it returns DerivedRequest instead: public override DerivedRequest request { get; set; } Does anyone have any ideas about how to make this work? 回答1: This isn't really a good way to structure things. Do one of the following 1) Just don't change the return