Java Generics - Bound Types Erasure


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Java Compiler replaces type parameters in generic type with their bound if bounded 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<Double> doubleBox = new Box<Double>();

      integerBox.add(new Integer(10));
      doubleBox.add(new Double(10.0));

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

class Box<T extends Number> {
   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 Number 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 doubleBox = new Box();

      integerBox.add(new Integer(10));
      doubleBox.add(new Double(10.0));

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

class Box {
   private Number t;

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

   public Number get() {
      return t;
   }   
}

In both case, result is same −

Output

Integer Value :10
Double Value :10.0


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