What are the design patterns for anonymous inner classes in Java?
Anonymous inner classes are special inner classes in Java that have no explicit name and are created through the new expression. They are mainly used to implement specific interfaces or extend abstract classes and are used immediately after creation. Common anonymous inner class design patterns include: Adapter pattern: converts one interface into another interface. Strategy Pattern: Defining and Replacement Algorithms. Observer pattern: Register observers and handle events. It is very useful in practical applications, such as sorting a TreeSet by string length, creating anonymous threads, etc.
Design pattern of Java anonymous inner class
Anonymous inner class is a special type of inner class in Java that does not explicit name, instead create it directly using a new expression. It is mainly used to implement a specific interface or extend a specific abstract class, and is usually created within the method body and used immediately.
Main design patterns
The following are common design patterns for using anonymous inner classes:
1. Adapter pattern
Adapter pattern Use anonymous inner classes to convert one interface into another. For example, the following code creates an anonymous inner class that adapts the Adaptee
class to the Target
interface:
Target target = new Target() { @Override public void request() { adaptee.specificRequest(); } };
2. Strategy Pattern
The Strategy pattern uses anonymous inner classes to define families of algorithms and make them interchangeable. For example, the following code creates an anonymous inner class that implements the Comparator
interface to compare the lengths of two strings:
Comparator<String> comparator = new Comparator<String>() { @Override public int compare(String s1, String s2) { return s1.length() - s2.length(); } };
3. Observer pattern
Observer pattern uses anonymous inner classes to register observers and handle events emitted by the topic. For example, the following code creates an anonymous inner class that implements the Observer
interface to observe the Subject
object:
Subject subject = new Subject(); Observer observer = new Observer() { @Override public void update(Subject subject) { // 处理主题更新 } }; subject.addObserver(observer);
Practical case
Example: Create a TreeSet with a Comparator
TreeSet requires its elements to be compared. The following code uses an anonymous inner class to define a custom comparator to sort strings based on their length:
Set<String> treeSet = new TreeSet<>(new Comparator<String>() { @Override public int compare(String s1, String s2) { return s1.length() - s2.length(); } });
Example: Create an anonymous thread
The following code uses anonymous The inner class creates and starts a thread in which a message is printed:
new Thread() { @Override public void run() { System.out.println("Hello from thread!"); } }.start();
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