Raw Type, Generic Type and Parameterized Type

Java Tutorials - Herong's Tutorial Examples - Version 7.03, by Dr. Herong Yang

Java Tutorials - Herong's Tutorial Examples

∟Generic Classes and Parameterized Types

∟Raw Type, Generic Type and Parameterized Type

This section provides a tutorial example on how legacy applications can continue to use raw types instead of parameterized types. But compiler will give you 'unchecked or unsafe operations' warnings.

What Is a Generic Type? A generic type is a generic class or interface that uses type parameters.

What Is a Parameterized Type? A parameterized type is a parameterized version of a generic class or interface. For example, Vector<String> is a parameterized type.

What Is a Raw Type? A raw type is a parameterized type with the parameter type argument omitted. For example, Vector is raw type.

Raw types are supported in Java to keep legacy applications working. In most cases, a raw type is equivalent a parameterized type with "Object" as the type argument.

Here is a legacy example that still uses a raw type of the Vector<E> generic class.

/* RawTypeTest.java
 - Copyright (c) 2014, HerongYang.com, All Rights Reserved.
 */
import java.util.*;
class RawTypeTest {
   public static void main(String[] a) {
      java.io.PrintStream o = System.out;

      Vector myList = new Vector();
      myList.add(new String("Milk"));
      myList.add(new Float(3.99));

      String name = (String) myList.get(0);
      Float price = (Float) myList.get(1);
      o.println(name+": "+price);
   }
}

Compile and run this example. You will get:

C:\herong>javac RawTypeTest.java

Note: RawTypeTest.java uses unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.

C:\herong>java RawTypeTest
Milk: 3.99

As you can see, the compiler let you to use raw types. But it gives you the "unchecked or unsafe operations" warning. If you recompile it with the "-Xlint", you will see more details:

C:\herong>javac -Xlint RawTypeTest.java

RawTypeTest.java:9: warning: [rawtypes] found raw type: Vector
      Vector myList = new Vector();
      ^
  missing type arguments for generic class Vector<E>
  where E is a type-variable:
    E extends Object declared in class Vector
RawTypeTest.java:9: warning: [rawtypes] found raw type: Vector
      Vector myList = new Vector();
                          ^
  missing type arguments for generic class Vector<E>
  where E is a type-variable:
    E extends Object declared in class Vector
RawTypeTest.java:10: warning: [unchecked] unchecked call to add(E) as
a member of the raw type Vector
      myList.add(new String("Milk"));
                ^
  where E is a type-variable:
    E extends Object declared in class Vector
RawTypeTest.java:11: warning: [unchecked] unchecked call to add(E) as
a member of the raw type Vector
      myList.add(new Float(3.99));
                ^
  where E is a type-variable:
    E extends Object declared in class Vector
4 warnings

Last update: 2014.

Table of Contents

About This Book

Installing JDK 1.8 on Windows

Execution Process, Entry Point, Input and Output

Primitive Data Types and Literals

Bits, Bytes, Bitwise and Shift Operations

Managing Bit Strings in Byte Arrays

Reference Data Types and Variables

StringBuffer - The String Buffer Class

System Properties and Runtime Object Methods

►Generic Classes and Parameterized Types