将泛型参数绑定到多个类型

通用参数也可以使用 T extends Type1 & Type2 & ... 语法绑定到多个类型。

假设你要创建一个类，其 Generic 类型应该同时实现 Flushable 和 Closeable，你可以编写

class ExampleClass<T extends Flushable & Closeable> {
}

现在，ExampleClass 只接受通用参数，类型同时实现 Flushable 和 Closeable。

ExampleClass<BufferedWriter> arg1; // Works because BufferedWriter implements both Flushable and Closeable

ExampleClass<Console> arg4; // Does NOT work because Console only implements Flushable
ExampleClass<ZipFile> arg5; // Does NOT work because ZipFile only implements Closeable

ExampleClass<Flushable> arg2; // Does NOT work because Closeable bound is not satisfied.
ExampleClass<Closeable> arg3; // Does NOT work because Flushable bound is not satisfied.

类方法可以选择将泛型类型参数推断为 Closeable 或 Flushable。

class ExampleClass<T extends Flushable & Closeable> {
    /* Assign it to a valid type as you want. */
    public void test (T param) {
        Flushable arg1 = param; // Works
        Closeable arg2 = param; // Works too.
    }

    /* You can even invoke the methods of any valid type directly. */
    public void test2 (T param) {
        param.flush(); // Method of Flushable called on T and works fine.
        param.close(); // Method of Closeable called on T and works fine too.
    }
}

注意：

你不能使用 OR （|）子句将泛型参数绑定到任一类型。仅支持 AND （&）子句。泛型类型只能扩展一个类和许多接口。类必须放在列表的开头。