Java Generics - Unbounded Types Erasure


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Java Compiler replaces type parameters in generic type with Object if unbounded type parameters are used.

Example

Live Demo
package com.tutorialspoint;

public class GenericsTester {
   public static void main(String[] args) {
      Box<Integer> integerBox = new Box<Integer>();
      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;
   }   
}

In this case, java compiler will replace T with Object class and after type erasure,compiler will generate bytecode for the following code.

Live Demo
package com.tutorialspoint;

public class GenericsTester {
   public static void main(String[] args) {
      Box integerBox = new Box();
      Box stringBox = new Box();

      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 {
   private Object t;

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

   public Object get() {
      return t;
   }   
}

In both case, result is same −

Output

Integer Value :10
String Value :Hello World


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