lombok-Delegate

本文主要介绍了Java中的委托以及lombok中Delegate注解。

首先看C#中的委托 https://www.runoob.com/csharp/csharp-delegate.html

重点

• C# 中的委托（Delegate）类似于 C 或 C++ 中函数的指针。委托（Delegate） 是存有对某个方法的引用的一种引用类型变量。引用可在运行时被改变。
• 委托的多播（Multicasting of a Delegate）
• 理解两个例子 https://projectlombok.org/features/Delegate.html

public class DelegationExample {
   private interface SimpleCollection {
     boolean add(String item);
     boolean remove(Object item);
   }

   private final Collection<String> collection = new ArrayList<String>();

   @SuppressWarnings("all")
   public boolean add(final String item) {
     return this.collection.add(item);
   }

   @SuppressWarnings("all")
   public boolean remove(final Object item) {
     return this.collection.remove(item);
   }

   public static void main(String[] args) {
       DelegationExample delegationExample = new DelegationExample();
       delegationExample.add("a"); // 实际上加入到了collection中了，也就是添加元素和删除元素委托给了collection来完成
   }
   
 }

使用Lombok的写法

public class DelegationExample {
    private interface SimpleCollection {
        boolean add(String item);
        boolean remove(Object item);
    }

    @Delegate(types=SimpleCollection.class)
    private final Collection<String> collection = new ArrayList<String>();

    public static void main(String[] args) {
       DelegationExample delegationExample = new DelegationExample();
       delegationExample.add("a"); // 实际上加入到了collection中了，也就是添加元素和删除元素委托给了collection来完成
    }
    /** 这部分代码被省略掉了
    @SuppressWarnings("all")
    public boolean add(final String item) {
        return this.collection.add(item);
    }

    @SuppressWarnings("all")
    public boolean remove(final Object item) {
        return this.collection.remove(item);
    }
    **/


 }

第二个例子,省了不少代码

class ExcludesDelegateExample {
  long counter = 0L;

  private interface Add {
    boolean add(String x);
    boolean addAll(Collection<? extends String> x);
  }

  private final Collection<String> collection = new ArrayList<String>();

  public boolean add(String item) {
    counter++;
    return collection.add(item);
  }

  public boolean addAll(Collection<? extends String> col) {
    counter += col.size();
    return collection.addAll(col);
  }

  @SuppressWarnings("all")
  public int size() {
    return this.collection.size();
  }

  @SuppressWarnings("all")
  public boolean isEmpty() {
    return this.collection.isEmpty();
  }

  @SuppressWarnings("all")
  public boolean contains(final Object arg0) {
    return this.collection.contains(arg0);
  }

  @SuppressWarnings("all")
  public java.util.Iterator<String> iterator() {
    return this.collection.iterator();
  }

  @SuppressWarnings("all")
  public Object[] toArray() {
    return this.collection.toArray();
  }

  @SuppressWarnings("all")
  public <T extends Object>T[] toArray(final T[] arg0) {
    return this.collection.<T>toArray(arg0);
  }

  @SuppressWarnings("all")
  public boolean remove(final Object arg0) {
    return this.collection.remove(arg0);
  }

  @SuppressWarnings("all")
  public boolean containsAll(final java.util.Collection<?> arg0) {
    return this.collection.containsAll(arg0);
  }

  @SuppressWarnings("all")
  public boolean removeAll(final java.util.Collection<?> arg0) {
    return this.collection.removeAll(arg0);
  }

  @SuppressWarnings("all")
  public boolean retainAll(final java.util.Collection<?> arg0) {
    return this.collection.retainAll(arg0);
  }

  @SuppressWarnings("all")
  public void clear() {
    this.collection.clear();
  }
}

class ExcludesDelegateExample {
  long counter = 0L;

  private interface Add {
    boolean add(String x);
    boolean addAll(Collection<? extends String> x);
  }

  @Delegate(excludes=Add.class)
  private final Collection<String> collection = new ArrayList<String>();

  public boolean add(String item) {
    counter++;
    return collection.add(item);
  }

  public boolean addAll(Collection<? extends String> col) {
    counter += col.size();
    return collection.addAll(col);
  }
}