BinaryOperator示例

在Java8中，BinaryOperator是一个函数接口，它集成BiFunction

BinaryOperator接收两个同样类型的实参，返回和参数同样类型的结果类型

BinaryOperator.java

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

BiFunction接收两个任意类型的实参，返回任意类型的结果

BiFunction.java

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

BinaryOperator

下面这个示例中，BiFunction<Integer, Integer, Integer>接收参数类型和返回结果的类型是一样的，因此可以用BianryOperator替换

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

输出

5
5

BinaryOperator作为参数

下面示例演示了使用stream.reduce()来对所有Integer进行求和

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); // 55Integer 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

55
55

IntBinaryOperator

如果数学操作基本数据类型，比如int，那么使用IntBinaryOperator可以获得更好的性能。

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); // 55int result2 = math((numbers), 0, Integer::sum);System.out.println(result2); // 55}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

55
55

BinaryOperator::maxBy()和BinaryOperator.minBy()

下面示例展示了使用BinaryOperator和自定义的比较器从开发者列表中找到薪资最好和最低的开发者

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 ComparatorComparator<Developer> comparing = Comparator.comparing(Developer::getSalary);// 2. BinaryOperator with a custom ComparatorBinaryOperator<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 payDeveloper developer = find(list, BinaryOperator.maxBy(Comparator.comparing(Developer::getSalary)));System.out.println(developer);  // Developer{name='jaden', salary=10000}// find developer with lowest payDeveloper 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

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

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

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BinaryOperator示例

BinaryOperator示例

BinaryOperator

BinaryOperator作为参数

IntBinaryOperator

BinaryOperator::maxBy()和BinaryOperator.minBy()

BinaryOperator示例相关推荐

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