superclass

How to inherit the constructor from a super class to a sub class? Constructors are not inherited, you must create a new, identically prototyped constructor in the subclass that maps to its matching constructor in the superclass. Here is an example of how this works: class Foo { Foo(String str) { } } class Bar extends Foo { Bar(String str) { // Here I am explicitly calling the superclass // constructor - since constructors are not inherited // you must chain them like this. super(str); } } Superclass constructor CAN'T be inherited in extended class. Although it can be invoked in extended class

I've been reading a lot about interfaces and class inheritance in Java, and I know how to do both and I think I have a good feel for both. But it seems that nobody ever really compares the two side by side and explains when and why you would want to use one or the other. I have not found a lot of times when implementing an interface would be a better system than extending a superclass. So when do you implement an interface and when do you extend a superclass? BalusC Use an interface if you want to define a contract . I.e. X must take Y and return Z. It doesn't care how the code is doing that.

I am trying to create a constructor that takes a field as a parameter, then puts it in a field that is stored in a superclass. Here is the code I am using public crisps(String flavour, int quantity) { this.flavour = super.getFlavour(); this.quantity = quantity; } In the superclass I have initialised the field with private String flavour; and I have an accessor method public String getFlavour() { return flavour; } I am getting an error " flavour has private access in the superclass ", but I believe this shouldn't matter as I am calling the accessor method that returns it to the field? What you

Lets suppose I have the following two classes public class alpha { public alpha(){ //some logic } public void alphaMethod1(){ //some logic } } public class beta extends alpha { public beta(){ //some logic } public void alphaMethod1(){ //some logic } } public class Test extends beta { public static void main(String[] args) { beta obj = new beta(); obj.alphaMethod1();// Here I want to call the method from class alpha. } } If I initiate a new object of type beta, how can I execute the alphamethod1 logic found in class alpha rather than beta? Can I just use super().alphaMethod1() <- I wonder if

I am really having a tough time understanding the wild card parameter. I have a few questions regarding that. ? as a type parameter can only be used in methods. eg: printAll(MyList<? extends Serializable>) I cannot define classes with ? as type parameter. I understand the upper bound on ? . printAll(MyList<? extends Serializable>) means: " printAll will print MyList if it has objects that implement the Serialzable interface. " I have a bit of an issue with the super . printAll(MyList<? super MyClass>) means: " printAll will print MyList if it has objects of MyClass or any class which extends

So say I have a subclass that extends a superclass. In what scenarios do I need to explicitly type super() to get the superclass constructor to run? I'm looking at an example in a book about abstract classes and when they extend it with a non-abstract subclass, the subclass's default constructor is blank and there's a comment that says the superclass's default constructor will be called. At the same time I've also seen instances on here where someone's problem was not explicitly calling super() . Is the distinction from calling the superclass's default/non-default constructor from the subclass