How to use generics in Java language

How to use generics in Java language

The Java language is a type-safe programming language, which means that it checks for type errors at compile time, thereby reducing errors that occur at runtime. The introduction of generics in Java 5 allows Java programmers to operate data types more flexibly, making huge improvements in type safety and code readability. This article will introduce the basic concepts and usage of Java language generics.

1. The concept of generics

Generics are a type parameterization mechanism in Java that supports writing a general code that can handle multiple types of data. Generics provide compile-time type checking and run-time type conversion support, which allows programmers to avoid type conversion errors and run-time exceptions.

The basic syntax of generics is as follows:

class MyClass<T> {
   T obj;
  …
}

Among them, "" is a type parameter, indicating that T is a type parameter and can be replaced by any data type. In the above example, obj is a generic object.

2. Advantages of generics

The main advantages of using generics include:

• Enhance the readability of the code.
• Enhance the reliability of the code because the compiler will check the type and reduce runtime type errors.
• Code reusability is higher because generics can be used to create generic code that can handle different types of data sets.
• Better support for type safety and type conversion.

3. The use of generics

The use of generics can be divided into generic classes, generic methods and generic interfaces. The following describes how to use these three situations respectively.

3.1 Generic class

A generic class is a class that declares one or more type variables. When defining a generic class, add "" after the class name to indicate that this is a class with type parameters.

For example:

class MyClass<T> {
   T value;
   public void setValue(T value){
      this.value = value;
   }
   public T getValue(){
      return value;
   }
}

In the above example, MyClass is a generic class, and "" means it is called a generic parameter. The parameters and return types in the setValue() and getValue() methods are both T types, which means that any data type can be used to fill the value variable.

3.2 Generic methods

A generic method is a method that has generic type parameters when declared. Using generic methods allows for more flexible and type-safe code.

For example:

class MyClass {
   public static <E> void printArray(E[] arr){
      for (E element : arr){
         System.out.println(element);
      }
   }
}

In the above example, the printArray() method uses a generic type parameter E, which can be called by passing arrays of different types.

3.3 Generic interface

A generic interface is an interface declared in the form of type parameters. You can use generic interfaces to define an interface that supports different types of data sets.

For example:

interface MyInterface<T> {
   void add(T element);
   T get(int index);
}

In the above example, MyInterface is a parameterized interface. In this interface, both the add() method and the get() method use the type parameter T to support Different types of data sets.

4. Generic type erasure

Generic type erasure means that at compile time, the Java compiler will replace all type parameters of the generic with their boundary types or Object type. This means that at run time, the concrete type information of a generic type parameter can no longer be accessed.

For example:

class Test<T> {
   T obj;
   public Test(T obj){
      this.obj = obj;
   }
   public T getObj(){
      return obj;
   }
}

In the above example, T will be erased into the Object type during compilation, so inside the compiler, the Test class actually looks like this:

class Test {
   Object obj;
   public Test(Object obj){
      this.obj = obj;
   }
   public Object getObj(){
      return obj;
   }
}

Therefore, the specific type information of type parameter T cannot be accessed at runtime.

5. Summary

Generics are a very useful feature in Java. It can improve the flexibility and readability of applications, while reducing type conversion errors and runtime exceptions. occur. When using generics, you need to pay attention to type erasure issues to avoid unexpected type conversion errors.

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