![]() ![]() or you could just require that you repeat the constructors from the superclass if you want to "inherit" them, which arguably is the more obvious way of doing it. ![]() In this guide we will see the use of super with variable, method and constructor. S.print() // throws NullPointerExceptionįrom this example, you see that you'd need some way of declaring that "I want to inherit these constructors" or "I want to inherit all constructors except for these", and then you'd also have to specify a default constructor inheritance preference just in case someone adds a new constructor in the superclass. The super keyword in java refers to the objects of immediate parent class. Sub s = new Sub("message") // Calling Super constructor - detail is never initialized! detail is never null, so this method won't fail It is not mandatory to explicitly call the parent constructor. If (detail = null) throw new NullPointerException() In this way, it first executes the parent class constructor, and then the child class constructor. So both the constructor needs to be executed because this object (subclass) contains member variables of both classes. In brief, the rules is: sub class constructor has to invoke super class instructor, either explicitly by programmer or. Therefore you get code that wont compile. The second super() would be the second line. The super constructor is defined, and good to invoke. A super() constructor call must be the first line in a constructor. The following code is OK: The Sub constructor explicitly call the super constructor with parameter. If (msg = null) throw new NullPointerException() Explicitly call super constructor in sub constructor. S.doSomeStuff() // throws ClassCastException Sub s = new Sub(Long.valueOf(666L)): // Devilish invocation of Super constructor! We know this.value is an Integer, so it's safe to cast.ÄoSomethingWithAnInteger((Integer)this.value) This video lesson on super keyword in java belongs to the, java tutorial for beginners playlist.what is super keyword The super keyword refers to superclass (parent) objects. You may not want clients of the subclass to be able to call certain constructors available in the superclass. Because constructing your subclass object may be done in a different way from how your superclass is constructed. ![]()
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