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使用Java8的Lambda实现的一个简单案例

   考虑下面这个场景:某个操作有预先处理和事后处理两个前后处理,这个操作执行依赖预期行为,预先处理释放出这个操作需要的参数,而事后处理做必要的清理工作。

首先,我们看看如何通过内部类来实现,首先定义一个接口表达需求的行为:

interface OldPerformer {

 

  public void performTask(String id, int status);

 

}

下面是预先处理Pre-Processing和事后处理Post-processing

public class PrePostDemo {

 

  static void performTask(String id, OldPerformer performer) {

    System.out.println("Pre-Processing...");

    System.out.println("Fetching the status for id: " + id);

    int status = 3;//Some status value fetched

    performer.performTask(id, status);

    System.out.println("Post-processing...");

  }

 

}

下面我们看看调用代码PrePostDemo中的main方法:

public static void main(String[] args) {

 

    //内部类需要final

    final String outsideOfImpl = "Common Value";

 

    //调用PrePostDemo.performTask方法

    performTask("1234", new OldPerformer() {

      @Override

      public void performTask(String id, int status) {

        System.out.println("Finding data based on id...");

        System.out.println(outsideOfImpl);

        System.out.println("Asserting that the status matches");

      }

 

    });

 

    //调用PrePostDemo.performTask方法

    performTask("4567", new OldPerformer() {

      @Override

      public void performTask(String id, int status) {

        System.out.println("Finding data based on id...");

        System.out.println(outsideOfImpl);

        System.out.println("Update status of the data found");

      }

    });

  }

}

输出:

Pre-Processing...
Fetching the status for id: 1234
Finding data based on id...
Common Value
Asserting that the status matches
Post-processing...

Pre-Processing..
Fetching the status for id: 4567
Finding data based on id...
Common Value
Update the status of the data found
Post-processing...

下面我们看看如何使用lambada表达式简单实现:

public class PrePostLambdaDemo {

 

  public static void main(String[] args) {  

    //不必定义final,但是一旦被lambda使用后不能变化。   

    String outsideOfImpl = "Common Value";

 

    doSomeProcessing("123", (String id, int status) -> {

      System.out.println("Finding some data based on"+id);

      System.out.println(outsideOfImpl);

      System.out.println("Assert that the status is "+status );

    });

 

    doSomeProcessing("456", (String id, int status) -> {

      System.out.print("Finding data based on id: "+id);

      System.out.println(outsideOfImpl);

      System.out.println("And updating the status: "+status);

    });

  }

 

  static void doSomeProcessing(String id, Performer performer ){

    System.out.println("Pre-Processing...");

    System.out.println("Finding status for given id: "+id);

    int status = 2;

    performer.performTask(id, status);

    System.out.println("Post-processing...");

  }

}

 

interface Performer{

public void performTask(String id, int status);

}

我们已经看到,区别于内部类,lambda表达式作用域之外的变量不必定义final,但是它是最终的final,也就是说被lambda使用后就不能再赋值变化了。当然,使用lambda表达式比内部类更干净。

 

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