Java generics, understanding these is enough.

Contents of this document:

1、 What are Java generics?

2、 Common generic writing examples

Generic class definition:

Define generic methods:

Use:

definition:

use:

III. type erasure

Let's take a look at an example. The operate class is as follows:

After decompilating the corresponding class file, we use Java GUI to decompile Exe view the compiled code as follows

No, there is no < string > part at all. This generic type limited to string type has been "erased". When writing code, the generic type will be verified. If the type does not correspond, it cannot be added, but the generic type is removed after compilation.

4、 What do you want to use Java generics

After the introduction of "type erasure" in the third part above, it is easier to say why Java generics should be used. The generic type here is equivalent to "three rules". First, set the "rules" for you. My list < string > is used for operation

String type, you can't insert the person object. To put it bluntly, it's for type safety. So the benefits are:

Type safety: by knowing the type limitations of variables defined using generics, the compiler can verify type assumptions to a much higher extent. Without generics, these assumptions exist only in the minds of programmers (or, if lucky, in code comments).

Eliminate cast:

Knowing so much about the above is enough to use generics on a daily basis. Let's look at the PECS principles

5、 Pecs principles

Let's start with an example:

Here, PECS principles are as follows:

PriorityQueue of Java queue series

A diagram shows various queues in Java

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