blocks|key|4702652|text|抽象类比默认方法实现(比如私有状态)要多得多，但是从Java8开始，只要您可以选择其中之一，就应该选择defender+(也就是。default)方法。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4702653|对默认方法的约束是，它只能通过调用其他接口方法来实现，而不能引用特定实现的状态。因此，主要的用例是更高级别和更方便的方法。|4702654|这个新特性的好处是，以前你被迫为方便的方法使用抽象类，从而将实现者限制为单继承，现在你可以有一个真正干净的设计，只需接口和最少的强制程序员的实现工作。|4702655|将default方法引入Java8的最初动机是希望在不破坏任何现有实现的情况下，使用面向lambda的方法扩展Collections+Framework接口。虽然这与公共库的作者更相关，但您可能会发现相同的功能在您的项目中也很有用。你已经有了一个集中的地方来添加新的便利，并且你不必依赖于类型层次结构的其余部分。|4702656|entityMap^0|1T|7|0|0|0|1|7|0^^$0|@$1|2|3|4|5|6|7|N|8|@$9|O|A|P|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|Q|8|@]|D|@]|E|$]]|$1|H|3|I|5|6|7|R|8|@]|D|@]|E|$]]|$1|J|3|K|5|6|7|S|8|@$9|T|A|U|B|C]]|D|@]|E|$]]|$1|L|3|-4|5|6|7|V|8|@]|D|@]|E|$]]]|M|$]]

There's a lot more to abstract classes than default method implementations (such as private state), but as of Java 8, whenever you have the choice of either, you should go with the defender (aka. <code>default</code>) method in the interface.

The constraint on the default method is that it can be implemented only in the terms of calls to other interface methods, with no reference to a particular implementation's state. So the main use case is higher-level and convenience methods.

The good thing about this new feature is that, where before you were forced to use an abstract class for the convenience methods, thus constraining the implementor to single inheritance, now you can have a really clean design with just the interface and a minimum of implementation effort forced on the programmer.

The original motivation to introduce <code>default</code> methods to Java 8 was the desire to extend the Collections Framework interfaces with lambda-oriented methods without breaking any existing implementations. Although this is more relevant to the authors of public libraries, you may find the same feature useful in your project as well. You've got one centralized place where to add new convenience and you don't have to rely on how the rest of the type hierarchy looks.

blocks|key|196765|text|请首先考虑开放/封闭原则。接口中的默认方法确实违反了它。这在Java中是一个不好的特性。它鼓励糟糕的设计，糟糕的架构，低软件质量。我建议完全避免使用默认方法。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|196766|问你自己几个问题:为什么你不能把你的方法放在抽象类中？那么你需要一个以上的抽象类吗？然后想想你的班级要对什么负责。您确定要放到单个类中的所有方法真的实现了相同的目的吗？也许你会区分几个目的，然后将你的类分成几个类，每个目的都有自己的类。|196767|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

Please think first of open/closed principle. The default methods in interfaces DO VIOLATE it. This is a bad feature in Java. It encourages bad design, bad architecture, low software quality. I would suggest to avoid using default methods completely.

Ask yourself a few questions:
Why can't you put your methods to the abstract class? Would you need then more than one abstract class? Then think about what is your class responsible for. Are you sure all methods you are going to put to the single class really fulfill the same purpose? May be you will distinguish several purposes and will then split your class into several classes, for each purpose its own class.

blocks|key|4702777|text|Java接口中的默认方法更多地用于提供函数的虚拟实现，从而使该接口的任何实现类不必声明所有抽象方法，即使它们只想处理一个抽象方法。因此，接口中的默认方法在某种程度上更多地取代了适配器类的概念。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4702778|然而，抽象类中的方法应该提供一个有意义的实现，只有在需要覆盖公共功能时，任何子类才应该覆盖该实现。|4702779|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

Default methods in Java Interface are to be used more for providing dummy implementation of a function thus saving any implementing class of that interface from the pain of declaring all the abstract methods even if they want to deal with only one.
Default methods in interface are thus in a way more a replacement for the concept of adapter classes.

The methods in abstract class are however supposed to give a meaningful implementation which any child class should override only if needed to override a common functionality.

blocks|key|196872|text|在业务用例上下文中，接口可用于定义特定的业务规则，其中抽象类将定义启动业务的公共结构。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|196873|假设某个企业主希望与亚马逊和沃尔玛合作，那么这里定义的接口将是WalmartPartner，AmazonPartner将定义特定的业务规则，而抽象类BusinessSetup将在特定区域中进行业务设置。|offset|length|style|CODE|196874|//+Interfaces
+
public+interface+WalmartPartner+{
++++public+static+boolean+signUpForWalmartBusinessAccount(String+BusinessId){
++++++++System.out.println("Setting+up+Walmart+Business+Partner");
++++++++return+true;
++++}
++++public+default++void++getWalmartDeals(){
++++++++System.out.println("Default+walmart+deal+executed+!");
++++}
++++public+abstract+void+setupShopifyForWalmart();
++++public+abstract++void+setupWalmartProducts();

public+interface+AmazonPartner+{
++++public+static+boolean+signUpAsAmazonServicePartner(String+BusinessId){
++++++++System.out.println("Setting+up+Amazon+Business+Partner");
++++++++return+true;
++++}
++++public+default++void++paymentPlatformSetup(){
++++++++System.out.println("+Amazon+default+payment+platform+is+setup");
++++}
++++public+abstract+void+setupPrimeMemberDealsByRegion();
++++public+abstract++void+setupPrimeDeals();
}

+//+Abstract+class+

public+abstract+class+BusinessSetup+{
++++String+businessId+;
++++public+BusinessSetup(String+businessId){
++++++++this.businessId+=+businessId;
++++++++System.out.println("1.+Initial+Business+setup+for+BusienssID:+"%2Bthis.businessId%2B"+is+Complete");
++++}
++++public+final+boolean+getBusinessRegisteredInRegion(String+region){
++++++++System.out.println("2.+Business+got+registered+in+"%2Bregion%2B+"!");
++++++++return+true;
++++}
++++public+abstract+void+setupCustomerPlatform(String+customerId);
++++public+abstract+void+setupVendorPlatform(String+vendorId);

}

//+Concrete+Class+
public+class+WalMartPartnerImpl+extends+BusinessSetup+implements+WalmartPartner+{
++++public+WalMartPartnerImpl(String+businessId)+{
++++++++super(businessId);
++++}
++++@Override
++++public+void+setupCustomerPlatform(String+customerId)+{
++++}

++++@Override
++++public+void+setupVendorPlatform(String+vendorId)+{
++++}

++++@Override
++++public+void+setupShopifyForWalmart()+{
++++}

++++@Override
++++public+void+setupWalmartProducts()+{
++++}
++++public+static+void+main(String+args[]){
++++++++WalMartPartnerImpl+walMartPartner+=+new+WalMartPartnerImpl("wal8989");
++++++++walMartPartner.getBusinessRegisteredInRegion("california");
++++++++walMartPartner.getWalmartDeals();
++++++++walMartPartner.setupCustomerPlatform("wal8989");

++++}
}|code-block|syntax|javascript|196875|entityMap^0|0|V|E|1A|D|22|D|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|P|8|@$D|Q|E|R|F|G]|$D|S|E|T|F|G]|$D|U|E|V|F|G]]|9|@]|A|$]]|$1|H|3|I|5|J|7|W|8|@]|9|@]|A|$K|L]]|$1|M|3|-4|5|6|7|X|8|@]|9|@]|A|$]]]|N|$]]

From a business use case context , Interfaces can be used to define specific business rules , where as abstract class would define the common structure to kickoff the business.
Say some business owner wants to partner with Amazon and Walmart , then the interfaces defined here would be <code>WalmartPartner</code> and <code>AmazonPartner</code> would define the specific business rules and the abstract class <code>BusinessSetup</code> will get the business setup in a specific region.
<pre><code>// Interfaces
 
public interface WalmartPartner {
 public static boolean signUpForWalmartBusinessAccount(String BusinessId){
 System.out.println(&quot;Setting up Walmart Business Partner&quot;);
 return true;
 }
 public default void getWalmartDeals(){
 System.out.println(&quot;Default walmart deal executed !&quot;);
 }
 public abstract void setupShopifyForWalmart();
 public abstract void setupWalmartProducts();

public interface AmazonPartner {
 public static boolean signUpAsAmazonServicePartner(String BusinessId){
 System.out.println(&quot;Setting up Amazon Business Partner&quot;);
 return true;
 }
 public default void paymentPlatformSetup(){
 System.out.println(&quot; Amazon default payment platform is setup&quot;);
 }
 public abstract void setupPrimeMemberDealsByRegion();
 public abstract void setupPrimeDeals();
}

 // Abstract class 

public abstract class BusinessSetup {
 String businessId ;
 public BusinessSetup(String businessId){
 this.businessId = businessId;
 System.out.println(&quot;1. Initial Business setup for BusienssID: &quot;+this.businessId+&quot; is Complete&quot;);
 }
 public final boolean getBusinessRegisteredInRegion(String region){
 System.out.println(&quot;2. Business got registered in &quot;+region+ &quot;!&quot;);
 return true;
 }
 public abstract void setupCustomerPlatform(String customerId);
 public abstract void setupVendorPlatform(String vendorId);

}

// Concrete Class 
public class WalMartPartnerImpl extends BusinessSetup implements WalmartPartner {
 public WalMartPartnerImpl(String businessId) {
 super(businessId);
 }
 @Override
 public void setupCustomerPlatform(String customerId) {
 }

 @Override
 public void setupVendorPlatform(String vendorId) {
 }

 @Override
 public void setupShopifyForWalmart() {
 }

 @Override
 public void setupWalmartProducts() {
 }
 public static void main(String args[]){
 WalMartPartnerImpl walMartPartner = new WalMartPartnerImpl(&quot;wal8989&quot;);
 walMartPartner.getBusinessRegisteredInRegion(&quot;california&quot;);
 walMartPartner.getWalmartDeals();
 walMartPartner.setupCustomerPlatform(&quot;wal8989&quot;);

 }
}
</code></pre>

Java 8 allows for default implementation of methods in interfaces called <a href="http://java.dzone.com/articles/introduction-default-methods" rel="noreferrer">Default Methods</a>.

I am confused between when would I use that sort of <code>interface default method</code>, instead of an <code>abstract class</code> (with <code>abstract method(s)</code>).

So when should interface with default methods be used and when should an abstract class (with abstract method(s)) be used? Are the abstract classes still useful in that scenario?

When to use: Java 8+ interface default method, vs. abstract method

Java

Java8允许在名为的接口中默认实现方法。我不知道什么时候才能使用那种interface default method，而不是abstract class (带有abstract method(s))。那么，什么时候应该使用缺省方法的接口，什么时候应该使用抽象类(使用抽象方法)？在这种情况下，抽象类还有用吗？

问何时使用: Java 8+接口默认方法与抽象方法
EN

社区

活动

资源

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问何时使用: Java 8+接口默认方法与抽象方法EN

社区

活动

资源

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问何时使用: Java 8+接口默认方法与抽象方法
EN