无涯教程-Java泛型 - 无限类型擦除

如果使用无限制的类型参数，则Java Compiler会将通用类型的类型参数替换为对象。

package com.learnfk;

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;
   }   
}

在这种情况下，java编译器将T用对象类替换，并且在类型擦除之后，编译器将为以下代码生成字节码。

package com.learnfk;

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;
   }   
}

在两种情况下，输出都是相同的-

Integer Value :10
String Value :Hello World

参考链接

https://www.learnfk.com/java-generics/java-generics-unbound-typeerasure.html