BinaryOperator函数式接口

不念不忘少年蓝@ 2022-12-24 00:55 280阅读 0赞

## 1.BinaryOperator的定义 ##

@FunctionalInterface
    public interface BinaryOperator<T> extends BiFunction<T, T, T> { 
        static <T> BinaryOperator<T> minBy(Comparator<? super T> comparator) { 
            Objects.requireNonNull(comparator);
            return (a, b) -> { 
                return comparator.compare(a, b) <= 0 ? a : b;
            };
        }
    
        static <T> BinaryOperator<T> maxBy(Comparator<? super T> comparator) { 
            Objects.requireNonNull(comparator);
            return (a, b) -> { 
                return comparator.compare(a, b) >= 0 ? a : b;
            };
        }
    }

*  从上面不难发现，BinaryOperator继承了BiFunction，并且多了二个静态方法minBy和maxBy。
 *  minBy和maxBy有很意思，返回了一个BiFunction对应的Lambda，Lambda内部使用传入的comparator比较器比较，然后在进一步处理返回最大值还是最小值。

## 2.更多例子 ##

public class BinaryOperatorTest { 
        public static void main(String[] args){ 
            BinaryOperatorTest test = new BinaryOperatorTest();
            test.testBinaryOperator(1,2,(num1,num2)->num1 + num2); //3
            test.testBinaryOperator(4,2,(num1,num2)->num1 - num2); //2
            test.testBinaryOperator(3,2,(num1,num2)->num1 * num2); //6
            test.testBinaryOperator(8,2,(num1,num2)->num1 / num2); //4
            test.testMinBy("hello","wonders",(str1,str2)->str1.length()-str2.length()); //hello
            //方法引用
            test.testMinBy("hello","wonders", Comparator.comparingInt(String::length)); //hello
            test.testMinBy("hello","wonders",(str1,str2)->str1.charAt(0)-str2.charAt(0)); //hello
            //方法引用
            test.testMinBy("hello","wonders", Comparator.comparingInt(str -> str.charAt(0))); //hello
            test.testMaxBy("hello","wonders",(str1,str2)->str1.length()-str2.length()); //wonders
            //方法引用
            test.testMaxBy("hello","wonders", Comparator.comparingInt(String::length)); //wonders
            test.testMaxBy("hello","wonders",(str1,str2)->str1.charAt(0)-str2.charAt(0)); //wonders
            //方法引用
            test.testMaxBy("hello","wonders", Comparator.comparingInt(str -> str.charAt(0))); //wonders
        }
    
        public void testBinaryOperator(Integer num1,Integer num2,BinaryOperator<Integer> result){ 
            System.out.println(result.apply(num1,num2));
        }
    
        /** * 返回两者里面较小的一个 * @param str1 * @param str2 * @param comparator */
        public void testMinBy(String str1, String str2, Comparator<String> comparator){ 
            System.out.println(BinaryOperator.minBy(comparator).apply(str1,str2));
        }
    
        /** * 返回两者里面较大的一个 * @param str1 * @param str2 * @param comparator */
        public void testMaxBy(String str1, String str2, Comparator<String> comparator){ 
            System.out.println(BinaryOperator.maxBy(comparator).apply(str1,str2));
        }
    }