Lecture 14: Interface

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分类专栏：软件工程文章标签： adt interface

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本文探讨了Java中接口的概念及其作为抽象数据类型的作用，并详细解释了子类型的关系及其实现方式。此外，还介绍了如何使用静态工厂方法来创建实例，并讨论了泛型接口的应用场景。

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1 Interface

Java’s interface is a useful language mechanism for expressing an abstract data type (ADT).

1.1 Subtypes

A subtype is simply a subset of the supertype : ArrayList and LinkedList are subtypes of List . “B is a subtype of A” means “every B is an A.” In terms of specifications: “every B satisfies the specification for A.”

How will clients use this ADT as an interface? Here’s an example:

SomeInterface s = new Subtypes(true);
System.out.println("The first character is: " + s.charAt(0));

This pattern breaks the abstraction barrier we’ve worked so hard to build between the abstract type and its concrete representations. Clients must know the name of the concrete representation class.
Fortunately, (as of Java 8) interfaces are allowed to contain static methods, so we can implement the creator operation valueOf as a static factory method in the interface， as an example:

public interface MyString {

    /** @param b a boolean value
     *  @return string representation of b, either "true" or "false" */
    public static MyString valueOf(boolean b) {
        return new FastMyString(true);
    }

2 Generic Interfaces

public interface Set<E> {
    // ...

Generic interface, non-generic implementation.

public class CharSet implements Set<Character>{
//...

Generic interface, generic implementation

public class HashSet<E> implements Set<E> {
//...

Reference

[1] 6.005 — Software Construction on MIT OpenCourseWare | OCW 6.005 Homepage at https://ocw.mit.edu/ans7870/6/6.005/s16/