![]() ![]() Let’s say you need to set the values while the object is being created like in the examples explained below. It adds some flexibility to the object construction. We use constructor overloading approach in Java to initialize the object in multiple different ways. Let us understand why do we need constructor overloading in Java. Now that we have seen how we do constructor overloading. Why use constructor overloading in Java ? Next let us understand why do we require constructor overloading in Java. In other words this is known as constructor overloading.Īnd we have 3 constructor overloads. public class Person () Code language: JavaScript ( javascript )Īs we can see that in the class above we have in total 3 constructors. In other words it is used to initialize the instance of an object. Yes, that is whenever you do a new YourClassName(). The constructor is invoked whenever you create an object of a class. Having said that, you cannot use constructor as a regular method on it’s resulting instance.Īre you are familiar with the new keyword in Java ? If you answered yes, then you are close to understanding what a constructor is. But a constructor’s primary function is entirely different. It’s main purpose is to perform some action in its own instance. ![]() And it’s name must be exactly as the name of the class. It doesn’t have a return type defined in its declaration. You may want to have another object that is responsible for creating the object through the builder pattern.A constructor in Java is a special method that is doesn’t behave like a normal method. That avoids polluting your package with another class which is only useful for building instances of Foo. Foo foo = new Foo.Builder().setName(.).setDescription(.).build() One option in the Java implementation of the builder pattern is to use a nested type, e.g. This allows you to build the whole final object in a fluent way. Note the comment above the constructor call in the final snippet - if your helper class is only ever helpful for creating objects of a single type, you can give it an extra method ( build, create, start, whatever is most appropriate) to take the place of the constructor call. The Java framework itself uses this approach in ProcessBuilder, although personally I'm not keen on the way it overloads method names to either return a value or set a value based on whether you provide an argument :( This is particularly useful if the main type you're constructing is an immutable type - it means you can apply conditional logic in the calling code to set some parameters but not others. Either a constructor call at the end, or give FooParameters Often it's useful to make the setters return the builder, so you can use: FooParameters parameters = new FooParameters() This should be mutable, with setters for all of the different values. ![]() That way you get consistency.Īnother option is to use a "parameter object" following the builder pattern - create another class whose sole purpose is to hold the data for the constructor parameters. If possible, chain the constructors together so that the default for any particular value is only specified in one place - or use a constant. You still end up with quite a lot of cruft in terms of overloaded constructors, but at least each of those "extra" constructors contains no actual code - just a call to another constructor. Public Foo(String name, String description) Assuming you're effectively applying defaults, usually the best approach is to have one "full" constructor and make the others call it. ![]()
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