Java Generics - Type Inference

Type inference represents the Java compiler's ability to look at a method invocation and its corresponding declaration to check and determine the type argument(s). The inference algorithm checks the types of the arguments and, if available, assigned type is returned. Inference algorithms tries to find a specific type which can fullfill all type parameters.

Compiler generates unchecked conversion warning in-case type inference is not used.

Syntax

Box<Integer> integerBox = new Box<>();

Where

• Box − Box is a generic class.

• <> − The diamond operator denotes type inference.

Description

Using diamond operator, compiler determines the type of the parameter. This operator is avalilable from Java SE 7 version onwards.

Example

Create the following java program using any editor of your choice.

GenericsTester.java

package com.howcodex;

public class GenericsTester {
   public static void main(String[] args) {
      //type inference   
      Box<Integer> integerBox = new Box<>();
      //unchecked conversion warning
      Box<String> stringBox = new Box<String>();

      integerBox.add(new Integer(10));
      stringBox.add(new String("Hello World"));

      System.out.printf("Integer Value :%d\n", integerBox.get());
      System.out.printf("String Value :%s\n", stringBox.get());
   }
}

class Box<T> {
   private T t;

   public void add(T t) {
      this.t = t;
   }

   public T get() {
      return t;
   }   
}

This will produce the following result.

Output

Integer Value :10
String Value :Hello World