How to understand java generics

Generics are a new feature of Java SE 1.5. The definition of generics in "Java Core Technology" is:

"Generics" means written code Can be reused by different types of objects.

It can be seen that generics are proposed to write more reusable code.

The essence of generics is a parameterized type, which means that the data type being operated is specified as a parameter.

For example, the common collection class LinkedList:

public class LinkedList<E> extends AbstractSequentialList<E> implements
    List<E>, Deque<E>, Queue<E>, Cloneable, Serializable {
//...
transient Link<E> voidLink;
//...

As you can see, there is a special part "" after the LinkedList class name and the interface name it implements. , and the type Link of its members also contains a "". This symbol is the type parameter, which allows different types to be passed in when creating a LinkedList at runtime, such as new LinkedList, so that its members are stored The type is also String.

In fact, the main goals of introducing generics are the following:

● Type safety

The main goals of generics The goal is to improve the type safety of Java programs

ClassCastException exceptions caused by incorrect Java types can be checked during compilation

In line with the principle that the earlier an error occurs, the smaller the cost

● Eliminate forced type conversions

A side benefit of generics is that you can directly get the target type when using it, eliminating many forced type conversions

What you get is what you need, which makes the code More readable and reduces the chance of errors

● Potential performance gains

Due to the way generics are implemented, supporting generics (almost) requires no JVM or classes File changes

All work is done in the compiler

The code generated by the compiler is almost the same as the code written without using generics (and casts), just more ensured Just type safety

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