Java 8 BinaryOperator示例

刺骨的言语ヽ痛彻心扉 2023-02-15 05:11 16阅读 0赞

在Java 8中， [BinaryOperator][]是一个功能接口，它扩展了`BiFunction` 。

`BinaryOperator`接受两个相同类型的参数，并返回其参数相同类型的结果。

BinaryOperator.java

@FunctionalInterface
    public interface BinaryOperator<T> extends BiFunction<T,T,T> {
    }

`BiFunction`接受两个任意类型的参数，并返回任意类型的结果。

BiFunction.java

@FunctionalInterface
    public interface BiFunction<T, U, R> {
          R apply(T t, U u);
    }

## 1. BinaryOperator ##

1.1在此示例中，可以使用`BinaryOperator<Integer>`替换接受并返回相同类型的`BiFunction<Integer, Integer, Integer>` `BinaryOperator<Integer>` 。

Java8BinaryOperator1.java

package com.mkyong;
    
    import java.util.function.BiFunction;
    import java.util.function.BinaryOperator;
    
    public class Java8BinaryOperator1 {
    
        public static void main(String[] args) {
    
            // BiFunction
            BiFunction<Integer, Integer, Integer> func = (x1, x2) -> x1 + x2;
    
            Integer result = func.apply(2, 3);
    
            System.out.println(result); // 5
    
            // BinaryOperator
            BinaryOperator<Integer> func2 = (x1, x2) -> x1 + x2;
    
            Integer result2 = func.apply(2, 3);
    
            System.out.println(result2); // 5
    
        }
    
    }

输出量

5
    5

## 2. BinaryOperator 作为论点 ##

2.1此示例模拟`stream.reduce()`求和所有`Integer` 。

Java8BinaryOperator2.java

package com.mkyong;
    
    import java.util.Arrays;
    import java.util.List;
    import java.util.function.BinaryOperator;
    
    public class Java8BinaryOperator2 {
    
        public static void main(String[] args) {
    
            Integer[] numbers = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
    
            Integer result = math(Arrays.asList(numbers), 0, (a, b) -> a + b);
    
            System.out.println(result); // 55
    
            Integer result2 = math(Arrays.asList(numbers), 0, Integer::sum);
    
            System.out.println(result2); // 55
    
        }
    
        public static <T> T math(List<T> list, T init, BinaryOperator<T> accumulator) {
            T result = init;
            for (T t : list) {
                result = accumulator.apply(result, t);
            }
            return result;
        }
    
    }

输出量

55
    55

## 3. IntBinaryOperator ##

3.1如果数学运算涉及基本类型（如`int` ，请更改为`IntBinaryOperator`以获得更好的性能。

Java8BinaryOperator3.java

package com.mkyong;
    
    import java.util.function.IntBinaryOperator;
    import java.util.stream.IntStream;
    
    public class Java8BinaryOperator3 {
    
        public static void main(String[] args) {
    
            int[] numbers = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
    
            int result = math((numbers), 0, (a, b) -> a + b);
    
            System.out.println(result); // 55
    
            int result2 = math((numbers), 0, Integer::sum);
    
            System.out.println(result2); // 55
    
            IntStream
        }
    
        public static int math(int[] list, int init, IntBinaryOperator accumulator) {
            int result = init;
            for (int t : list) {
                result = accumulator.applyAsInt(result, t);
            }
            return result;
        }
    
    }

输出量

55
    55

## 4. BinaryOperator.maxBy（）和BinaryOperator.minBy（） ##

4.1本示例使用`BinaryOperator`和自定义的`Comparator`从开发人员列表中找到收入最高和最低的开发人员。

Java8BinaryOperator4.java

package com.mkyong;
    
    import java.math.BigDecimal;
    import java.util.Arrays;
    import java.util.Comparator;
    import java.util.List;
    import java.util.function.BinaryOperator;
    
    public class Java8BinaryOperator4 {
    
        public static void main(String[] args) {
    
            Developer dev1 = new Developer("jordan", BigDecimal.valueOf(9999));
            Developer dev2 = new Developer("jack", BigDecimal.valueOf(8888));
            Developer dev3 = new Developer("jaden", BigDecimal.valueOf(10000));
            Developer dev4 = new Developer("ali", BigDecimal.valueOf(2000));
            Developer dev5 = new Developer("mkyong", BigDecimal.valueOf(1));
    
            List<Developer> list = Arrays.asList(dev1, dev2, dev3, dev4, dev5);
    
            // 1. Create a Comparator
            Comparator<Developer> comparing = Comparator.comparing(Developer::getSalary);
    
            // 2. BinaryOperator with a custom Comparator
            BinaryOperator<Developer> bo = BinaryOperator.maxBy(comparing);
    
            Developer result = find(list, bo);
    
            System.out.println(result);     // Developer{name='jaden', salary=10000}
    
            // one line
    
            // find developer with highest pay
            Developer developer = find(list, BinaryOperator.maxBy(Comparator.comparing(Developer::getSalary)));
            System.out.println(developer);  // Developer{name='jaden', salary=10000}
    
            // find developer with lowest pay
            Developer developer2 = find(list, BinaryOperator.minBy(Comparator.comparing(Developer::getSalary)));
            System.out.println(developer2); // Developer{name='mkyong', salary=1}
    
        }
    
        public static Developer find(List<Developer> list, BinaryOperator<Developer> accumulator) {
            Developer result = null;
            for (Developer t : list) {
                if (result == null) {
                    result = t;
                } else {
                    result = accumulator.apply(result, t);
                }
            }
            return result;
        }
    
    }

Developer.java

package com.mkyong;
    
    import java.math.BigDecimal;
    
    public class Developer {
    
        String name;
        BigDecimal salary;
    
        public Developer(String name, BigDecimal salary) {
            this.name = name;
            this.salary = salary;
        }
    
        //...
    }

输出量

Developer{name='jaden', salary=10000}
    Developer{name='jaden', salary=10000}
    Developer{name='mkyong', salary=1}

## 参考文献 ##

*  [二进制运算符][BinaryOperator]
 *  Java 8 Lambda：比较器示例
 *  [Java 8 Stream.reduce（）示例][Java 8 Stream.reduce]
 *  [BiFunction JavaDoc][]
 *  [Java 8函数示例][Java 8]
 *  Java 8教程

标签： [双功能][Link 1] [Binaryoperator][] [比较器][Link 2] [功能接口][Link 3] [高阶功能][Link 4] [Java 8][Java 8 1] [sum][]

> 翻译自: [https://mkyong.com/java8/java-8-binaryoperator-examples/][https_mkyong.com_java8_java-8-binaryoperator-examples]

[BinaryOperator]: https://docs.oracle.com/javase/8/docs/api/java/util/function/BinaryOperator.html
[Java 8 Stream.reduce]: https://mkyong.com/java8/java-8-stream-reduce-examples/
[BiFunction JavaDoc]: https://docs.oracle.com/javase/8/docs/api/java/util/function/BiFunction.html
[Java 8]: https://mkyong.com/java8/java-8-function-examples/
[Link 1]: https://mkyong.com/tag/bifunction/
[Binaryoperator]: https://mkyong.com/tag/binaryoperator/
[Link 2]: https://mkyong.com/tag/comparator/
[Link 3]: https://mkyong.com/tag/functional-interface/
[Link 4]: https://mkyong.com/tag/higher-order-function/
[Java 8 1]: https://mkyong.com/tag/java-8/
[sum]: https://mkyong.com/tag/sum/
[https_mkyong.com_java8_java-8-binaryoperator-examples]: https://mkyong.com/java8/java-8-binaryoperator-examples/