![]() This is the initialization block that runs when an instanceĬheck(position. Kotlin also lets us create an initialization block that runs immediately after our properties have been set. We aren’t limited to just setting properties in a constructor. This lets use print Bob’s position in the println statement. Since we used the val keyword in front of the position argument, Kotlin created a position property on Bob. When we create an instance of Bob, we have to supply a String to the constructor. This primary constructor has two properties: name and roll. In the example of the User class, we had a primary constructor. Here, (val name: String, var roll: Int), is the primary Constructor. Kotlin has two ways of declaring a constructor. Notice how the Bob class has a position parameter of type String. In Kotlin language, the Constructor is declared with the class header, unlike Java, where you have to declare the Constructor in the class body. We can also define constructors that force us to use valid data. When we create a ChalkBoard object, we just use the () for the default constructor. When no constructor is specified, Kotlin will supply an empty no argument constructor. Let’s walk through the various forms of constructors we can define in Kotlin. Key points A class can have zero or more secondary class constructors A secondary constructor must call the primary constructor this can happen by directly. The other constructor takes an existing collection object and automatically adds all objects contained in the collection passed into the constructor into the new list. The first constructor is called the default constructor and accepts no arguments. The above Java code snippet demonstrates multiple constructor. Let’s consider the constructor found in the ArrayList class found in .ĪrrayList list = new ArrayList() //Default constructorĪrrayList list2 = new ArrayList(list) //Secondary constructor Like all methods, constructors can have zero or more parameters. The constructor runs when an instance of a class is created. Here, (val name: String, var roll: Int), is the primary Constructor. Such code is referred to as a constructor method. In Kotlin language, the Constructor is declared with the class header, unlike Java, where you have to declare the Constructor in the class body. Many OOP languages have special code that is used to initialize a class to a valid state. ![]()
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