Java – Using parent constructor in a child class in Java

constructorjava

I have a class "ChildClass" that extends the class "ParentClass". Rather than completely replace the constructor for the parent class, I want to call the parent class's constructor first, and then do some extra work.

I believe that by default the parent class's 0 arguments constructor is called. This isn't what I want. I need the constructor to be called with an argument. Is this possible?

I tried

this = (ChildClass) (new  ParentClass(someArgument));

but that doesn't work because you can't modify "this".

Best Answer

You can reference the parent's constructor with "super", from within a child's constructor.

public class Child extends Parent {
    public Child(int someArg) {
        super(someArg);
        // other stuff
    }
    // ....
}

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C# – Calling the base constructor in C#

Modify your constructor to the following so that it calls the base class constructor properly:

public class MyExceptionClass : Exception
{
    public MyExceptionClass(string message, string extrainfo) : base(message)
    {
        //other stuff here
    }
}

Note that a constructor is not something that you can call anytime within a method. That's the reason you're getting errors in your call in the constructor body.

Java – What are the differences between a HashMap and a Hashtable in Java

There are several differences between HashMap and Hashtable in Java:

Hashtable is synchronized, whereas HashMap is not. This makes HashMap better for non-threaded applications, as unsynchronized Objects typically perform better than synchronized ones.
Hashtable does not allow null keys or values. HashMap allows one null key and any number of null values.
One of HashMap's subclasses is LinkedHashMap, so in the event that you'd want predictable iteration order (which is insertion order by default), you could easily swap out the HashMap for a LinkedHashMap. This wouldn't be as easy if you were using Hashtable.

Since synchronization is not an issue for you, I'd recommend HashMap. If synchronization becomes an issue, you may also look at ConcurrentHashMap.

Best Answer

Related Solutions

C# – Calling the base constructor in C#

Java – What are the differences between a HashMap and a Hashtable in Java

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