Java 8 |收集器平均值(带示例)

原文:https://www . geesforgeks . org/Java-8-collectors-averaging int-in-Java-with-examples/

采集者平均积分(到功能<？super T > mapper) 方法用于查找参数中传递的整数的平均值。此方法返回一个收集器，该收集器生成应用于输入元素的整数值函数的算术平均值。如果没有元素作为输入元素传递，则此方法返回 0。

该方法计算算术平均值的公式为:

{\displaystyle A={\frac {1}{n}}\sum _{i=1}^{n}a_{i}={\frac {a_{1}+a_{2}+\cdots +a_{n}}{n}}}

语法:

public static 
   <T> Collector<T, ?, Double> 
     averagingInt(ToIntFunction<? super T> mapper)

哪里，

  • 接口收集器< T、A、R > :一种将输入元素累加到一个可变结果容器中的可变约简操作，可选地在所有输入元素都被处理之后将累加的结果转换为最终表示。还原操作可以顺序执行，也可以并行执行。
    • T: 归约运算的输入元素类型。
    • A: 还原操作的可变累加类型。
    • R: 归约运算的结果类型。
  • Double:Double 类在对象中包装一个基元类型 Double 的值。类型为 double 的对象包含类型为 Double 的单个字段。
  • to function:表示产生整数值结果的函数。

参数:该方法采用强制参数映射器，类型为到功能。它是一个从流中提取整型值的函数。

以下是说明 averagingInt()方法的示例:

程序 1:

// Java code to show the implementation of
// Collectors averagingInt(ToIntFunction mapper) function

import java.util.stream.Collectors;
import java.util.stream.Stream;

class GFG {

    // Driver code
    public static void main(String[] args)
    {

        // creating a string stream with numbers
        Stream<String> s = Stream.of("3", "4", "5");

        // using Collectors averagingInt(ToIntFunction mapper)
        // method to find arithmetic mean of inputs given
        double ans = s
                         .collect(Collectors
                                      .averagingInt(
                                          num -> Integer.parseInt(num)));

        // displaying the result
        System.out.println(ans);
    }
}

Output:

4.0

程序 2: 当没有输入元素作为参数传递给 averagingInt()方法时。

// Java code to show the implementation of
// Collectors averagingInt(ToIntFunction mapper) function

import java.util.stream.Collectors;
import java.util.stream.Stream;

class GFG {

    // Driver code
    public static void main(String[] args)
    {
        // creating a empty string stream
        Stream<String> s = Stream.of();

        // using Collectors averagingInt(ToIntFunction mapper)
        // method to find arithmetic mean of inputs given
        double ans = s
                         .collect(Collectors
                                      .averagingInt(
                                          num -> Integer.parseInt(num)));

        // displaying the result
        System.out.println(ans);
    }
}

Output:

0.0

程序 3:

// Java code to show the implementation of
// Collectors averagingInt(ToIntFunction mapper) function

import java.util.stream.Collectors;
import java.util.stream.Stream;

class GFG {

    // Driver code
    public static void main(String[] args)
    {
        // creating a string stream
        Stream<String> s = Stream.of("7", "8", "9", "10");

        // using Collectors averagingInt(ToIntFunction mapper)
        // method to find arithmetic mean of inputs given
        double ans = s
                         .collect(Collectors
                                      .averagingInt(
                                          num -> Integer.parseInt(num)));

        // displaying the result
        System.out.println(ans);
    }
}

Output:

8.5

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