Java – Constructor Injection, design for testability

constructor-injectionjavatestability

I have this code (you probably can ignore that it is Swing code), but I usually end up with too many arguments in my constructor. Should I use model bean class and then pass that object in the constructor?

public BrowserFrame(final JTextField url, final JTextArea response, final JTextField command, final JButton actionButton) {

    this.urlField = url;
    this.responseArea = response;
    this.commandField = command;
    this.actionButton = actionButton;

}

In this code, I am considering adding more objects, used by this class. Do I keep just adding more args and pass them in the constructor. Possibly use setting injection?

But according to Misko, this is also code smell.

http://misko.hevery.com/code-reviewers-guide/

"Objects are passed in but never used directly (only used to get access to other objects)"

Best Solution

Having too many arguments in your constructor is a sign that your class has too many responsibilities. If you're just setting fields in your constructor, look to see if some of those fields are only used by a subset of the methods in the class. That's a sign that your arguments and methods can be split up into smaller classes with more focused responsibility.

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Java – How does the Java ‘for each’ loop work

for (Iterator<String> i = someIterable.iterator(); i.hasNext();) {
    String item = i.next();
    System.out.println(item);
}

Note that if you need to use i.remove(); in your loop, or access the actual iterator in some way, you cannot use the for ( : ) idiom, since the actual iterator is merely inferred.

As was noted by Denis Bueno, this code works for any object that implements the Iterable interface.

Also, if the right-hand side of the for (:) idiom is an array rather than an Iterable object, the internal code uses an int index counter and checks against array.length instead. See the Java Language Specification.

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Yes, an abstract class can have a constructor. Consider this:

abstract class Product { 
    int multiplyBy;
    public Product( int multiplyBy ) {
        this.multiplyBy = multiplyBy;
    }

    public int mutiply(int val) {
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    }
}

class TimesTwo extends Product {
    public TimesTwo() {
        super(2);
    }
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class TimesWhat extends Product {
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The superclass Product is abstract and has a constructor. The concrete class TimesTwo has a constructor that just hardcodes the value 2. The concrete class TimesWhat has a constructor that allows the caller to specify the value.

Abstract constructors will frequently be used to enforce class constraints or invariants such as the minimum fields required to setup the class.

NOTE: As there is no default (or no-arg) constructor in the parent abstract class, the constructor used in subclass must explicitly call the parent constructor.

Best Solution

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