深入理解 Java 泛型
什么是泛型
Java 泛型（generics）是 JDK 5 中引入的特性。
为什么要引入泛型机制呢？
回答这个问题前，先让我们来看一个示例。
public class NoGenericsDemo {
public static void main(String[] args) {
List list = new ArrayList<>();
list.add("abc");
list.add(18);
list.add(new double[] {1.0, 2.0});
Object obj1 = list.get(0);
Object obj2 = list.get(1);
Object obj3 = list.get(2);
System.out.println("obj1 = [" + obj1 + "]");
System.out.println("obj2 = [" + obj2 + "]");
System.out.println("obj3 = [" + obj3 + "]");
int num1 = (int)list.get(0);
int num2 = (int)list.get(1);
int num3 = (int)list.get(2);
System.out.println("num1 = [" + num1 + "]");
System.out.println("num2 = [" + num2 + "]");
System.out.println("num3 = [" + num3 + "]");
}
}
// Output:
// obj1 = [abc]
// obj2 = [18]
// obj3 = [[D@47089e5f]
// Exception in thread "main" java.lang.ClassCastException: java.lang.String cannot be cast to java.lang.Integer
// at io.github.dunwu.javacore.generics.NoGenericsDemo.main(NoGenericsDemo.java:23)
...大约 12 分钟