We don’t need to do type-casting and we can remove ClassCastException at runtime. Notice the use of GenericsType class in the main method. GenericsType type1 = new GenericsType() //raw type Now we will use java generic class to rewrite the same class as shown below. Notice that while using this class, we have to use type casting and it can produce ClassCastException at runtime. String str = (String) type.get() //type casting, error prone and can cause ClassCastException GenericsTypeOld type = new GenericsTypeOld() To understand the benefit, let’s say we have a simple class as: package We use angle brackets () to specify the type parameter. A generic type is a class or interface that is parameterized over types. We can define our own classes with generics type. Also notice that in for loop, we don’t need typecasting of the element in the list, hence removing the ClassCastException at runtime. So if we try to add any other type of object in the list, the program will throw compile-time error. Notice that at the time of list creation, we have specified that the type of elements in the list will be String. no type casting needed, avoids ClassCastException list1.add(new Integer(5)) //compiler error List list1 = new ArrayList() // java 7 ? List list1 = new ArrayList() After Java 5, we use collection classes like below.
Another word for running a business code#
type casting leading to ClassCastException at runtimeĪbove code compiles fine but throws ClassCastException at runtime because we are trying to cast Object in the list to String whereas one of the element is of type Integer. Let’s see how generics help us using collection classes safely.
The whole collection framework was re-written to use generics for type-safety. Generics was added in Java 5 to provide compile-time type checking and removing risk of ClassCastException that was common while working with collection classes. We will look into below topics of generics in java. Understanding generics can become confusing sometimes if we go with jargon words, so I would try to keep it simple and easy to understand. We will try to learn the features of generics in this article. Generics in Java with collection classes is very easy but it provides a lot more features than just creating the type of collection. If you have been working on Java Collections and with version 5 or higher, I am sure that you have used it. Java Genrics is one of the most important features introduced in Java 5.
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