Generics - Introduction to Generics

Introduction to Generics

Let’s take an example to illustrate what generics are.
There are two classes as follows. It is necessary to construct objects of the two classes and print out their respective members x.
public class StringFoo {
  private String x;
  public String getX() {
      return x;
  }

  public void setX(String x) {
      this.

public class DoubleFoo {
private Double x;
public Double getX() {
return x;
}

public void setX(Double x) {
this.x = x;
}
}
If you want to implement the ong, Date, etc. It is really boring to write corresponding classes for type operations.
Therefore, refactor the above two classes into one class, consider the following:
In the above class, the logic of the members and methods are the same, but the types are different. Object is the parent class of all classes, so you can consider using Object as the member type, so that it can be universal.
public class ObjectFoo {
  private Object x;
  public Object getX() {
      return x;
  }

  public void setX(Object x) {
    this.

The calling code is as follows ：
public class ObjectFooDemo {
public static void main(String args[]) {
ObjectFoo strFoo = new ObjectFoo();
strFoo.setX("Hello Generics!");
ObjectFoo douFoo = new ObjectFoo() ;
                                                                                                                                                                                                                                                                                                   .setX(new Double("33"));
ObjectFoo objFoo = new ObjectFoo();
objFoo.setX(new Object());

String str = (String)strFoo.getX();
Double d = (Double)douFoo.getX();
Object obj = objFoo.getX();

System.out.println("strFoo.getX=" + str);
System.out.println("douFoo.getX=" + d);
System.out.println("strFoo.getX=" + obj);
}
}
The above is the code we wrote without generics, using the top-level base class Object for type declaration , and then pass the value in, and perform forced type conversion when taking it out.
JDK has introduced the concept of generics since 1.5 to elegantly solve such problems. Using generic technology, the code written is as follows:
public class GenericsFoo {
  private T x;
  public T getX() {
    return x;
  }

  public void setX(T x) {
     this. x = x;
}
}

The calling code is as follows:
public class GenericsFooDemo {
public static void main(String args[]){
GenericsFoo strFoo=new GenericsFoo();
           strFoo. setX("Hello Generics!");
        GenericsFoo douFoo=new GenericsFoo(); new GenericsFoo