The role of generics, and the difference with Object

Before Java SE 1.5, in the absence of generics, the parameter "arbitrary" was realized by reference to the type Object. The disadvantage of "arbitrary" was to do explicit mandatory type conversion , and this The conversion is required when the developer can predict the actual parameter type. For the case of forced type conversion errors, the compiler may not prompt the error, and the exception occurs only at runtime, which is a safety hazard.

public  class Gen <T> {  
     private T ob; // Define generic member variables   
  
    public Gen (T ob) {  
         this .ob = ob;   
    }   
  
    public T getOb () {  
         return ob;   
    }   
  
    public  void setOb (T ob) {  
         this .ob = ob;   
    }   
  
    public  void showType () {   
        System.out.println ( "The actual type of T is:" + ob.getClass (). getName ());   
    }   
}  

public  class GenDemo {  
     public  static  void main (String [] args) {  
         // Define an Integer version of the generic class Gen   
        Gen <Integer> intOb = new Gen <Integer> (88 );   
        intOb.showType ();   
        int i = intOb.getOb ();   
        System.out.println ( "value =" + i);   
        System.out.println ( "----------------------- ----------- " );  
         // Define a String version of the generic class Gen   
        Gen <String> strOb = new Gen <String> (" Hello Gen! " );   
        StrOb.showType ();   
        String s = strOb.getOb();  
        System.out.println("value= " + s);  
    }  
}  

 

 

 

 

In a word
, the benefit of generics is that type safety is checked at compile time , and all coercion is automatic and implicit , which improves the code reuse rate and does not have to be forced like Object.