Lambda表达式

1.常见单方法接口

  • Comparator
  • Runnable
  • Callable
普通:
String [] names={"mushroom","peach","appl","banana"}; Comparator comparator=new Comparator<String>() { @Override public int compare(String o1, String o2) { return o1.length()-o2.length(); //[appl, peach, banana, mushroom] } };
Lambda方式:
    
      Comparator<String> comparator=(String name1,String name2)->name1.length()-name2.length(); //[appl, peach, banana, mushroom]

Comparator<String> comparator=(name1 , name2)->name1.length()-name2.length(); //[appl, peach, banana, mushroom]
 

 

2. @FunctionalInterface

只定义了单方法的接口称之为FunctionalInterface,用注解@FunctionalInterface标记,如Callable接口

 * @see Executor
 * @since 1.5
 * @author Doug Lea
 * @param <V> the result type of method {@code call}
 */
@FunctionalInterface
public interface Callable<V> {
    /**
     * Computes a result, or throws an exception if unable to do so.
     *
     * @return computed result
     * @throws Exception if unable to compute a result
     */
    V call() throws Exception;
}

但 Comparator接口:

@FunctionalInterface
public interface Comparator<T> {

    int compare(T o1, T o2);

    boolean equals(Object obj);

    default Comparator<T> reversed() {
        return Collections.reverseOrder(this);
    }

    default Comparator<T> thenComparing(Comparator<? super T> other) {
        ...
    }
    
}

 

虽然Comparator接口有很多方法,但只有一个抽象方法int compare(T o1, T o2),其他的方法都是default方法或static方法。另外注意到boolean equals(Object obj)Object定义的方法,不算在接口方法内。因此,Comparator也是一个FunctionalInterface

 

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