Demonstrate a raw generic type.

 
/*
Java 2, v5.0 (Tiger) New Features
by Herbert Schildt
ISBN: 0072258543
Publisher: McGraw-Hill/Osborne, 2004
*/

class Gen<T> {  
  T ob; // declare an object of type T  
    
  // Pass the constructor a reference to   
  // an object of type T.  
  Gen(T o) {  
    ob = o;  
  }  
  
  // Return ob.  
  T getob() {  
    return ob;  
  }  
}  
  
// Demonstrate raw type. 
public class RawDemo {  
  public static void main(String args[]) {  
 
    // Create a Gen object for Integers. 
    Gen<Integer> iOb = new Gen<Integer>(88);  
   
    // Create a Gen object for Strings. 
    Gen<String> strOb = new Gen<String>("Generics Test");  
  
    // Create a raw-type Gen object and give it 
    // a Double value. 
    Gen raw = new Gen(new Double(98.6)); 
 
    // Cast here is necessary because type is unknown. 
    double d = (Double) raw.getob(); 
    System.out.println("value: " + d); 
 
    // The use of a raw type can lead to runtime. 
    // exceptions.  Here are some examples. 
 
    // The following cast causes a runtime error! 
//    int i = (Integer) raw.getob(); // runtime error 
 
    // This assigment overrides type safety. 
    strOb = raw; // OK, but potentially wrong 
//    String str = strOb.getob(); // runtime error  
     
    // This assignment also overrides type safety. 
    raw = iOb; // OK, but potentially wrong 
//    d = (Double) raw.getob(); // runtime error 
  }  
}

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Demonstrate a raw generic type. : Generic Parameter « Generics « Java

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