使用 Stream API 和示例在Java 8+ 中进行函数式编程

API 是应用程序编程接口的首字母缩写词，它是软件和Java流在数据源上工作。考虑一条小溪，就像一条小运河中的水流。让我们举一个现实生活中的例子。每次用户使用应用程序时，WhatsApp 都会流行起来，以便通过向其他用户发送短信或电话进行交流。两个用户都在使用 API。

Java流处理三种操作，如下所述

1. 数据源
2. 中间操作
3. 终端操作

方法：可以通过三种方式创建流

1. 使用集合框架中任何类的对象
2. 使用引用数据类型的数组
3. 使用“Java.util.stream”包中定义的接口

方法一：数据源

数据源可以多种多样，例如数组、列表等

句法：

ArrayList numbers = new ArrayList<>();
Integer[] numbers = {1,2,3};

示例 1：使用对象作为数据源

Java

// Java Program showcasing data source
// using an object as a data source
 
// Importing input output classes
import java.io.*;
 
// Class
class GFG {
 
    // Main driver method
    public static void main(String[] args)
    {
        // Data Source
 
        // Creating an arrayList object
        // Declaring object of String type
        ArrayList gfgNames = new ArrayList<>();
 
        // Custom input elements to above object
        gfgNames.add("Dean");
        gfgNames.add("castee");
        gfgNames.add("robert");
 
        // Creating object of Stream where Stream is created
        // using arrayList and object as data source
        Stream streamOfNames = gfgNames.stream();
 
        // Print and display element
        System.out.print(streamOfNames);
    }
}

示例 2：使用数组作为数据源

// Data Source
Integer[] numbers = {1,2,3,4,5};

// Stream using an array
Stream streamOfNumbers = Arrays.stream(numbers);

// using predefined Instream interface
integerStream = IntStream.range(1,100); // a stream from 1 to 99;

Java

// Java Program showcasing data source
// using an array as a data source
 
// Importing java input output class
import java.io.*;
 
// Importing all classes from
// java.util package
import java.util.*;
 
// Importing class for additional operations,
// additionls and pipelines
import java.util.stream.IntStream;
 
// Class
class GFG {
 
    // Main driver method
    public static void main(String[] args)
    {
        // Creating a predefined stream using range method
        // Custom inputs for range as parameters
        var stream = IntStream.range(1, 100);
 
        // Stream is created
        var max = stream.filter(number -> number % 4 == 0)
                      .count();
 
        // Print and display the maximum number
        // from the stream
        System.out.println(max);
    }
}

24

方法二：中间操作

中间操作是一些可以应用于流的方法。

Note: It can be of any number

filter()

例子：

Java

import java.io.*;
 
class GFG {
    public static void main(String[] args)
    {
        // Data Source
        Integer[] numbers = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 0 }
 
        // Stream
        Stream streamOfNumbers
            = Arrays.stream(numbers);
 
        // filter all the even numbers
        Stream evenNumbersStream
            = streamOfNumbers.filter(
                number -> number % 2 == 0)
    }
}

方法三：终端操作

我们可以在流上应用的终端操作方法会导致流被“关闭”。

概念：

一些终端操作可用于迭代流的元素。

min(),max(),count()

forEach(),noneMatch()

示例 1：解释流 API

Java

// Importing input output classes
import java.io.*;
// Importing all classes from
// java.util package
import java.util.*;
 
// Class
class GFG {
 
    // Main driver method
    public static void main(String[] args)
    {
        // Data source
        // Custom integer inputs
        Integer[] numbers
            = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 0 };
 
        // Stream
        var streamOfNumbers = Arrays.stream(numbers);
 
        // Using filter method
        var evenNumbersStream
            = streamOfNumbers
                  .filter(number -> number % 3 == 0)
                  .count();
 
        // Print and display
        System.out.println(evenNumbersStream);
    }
}

输出

4

示例 2：

Java

// Importing all classes from java.util package
import java.io.*;
import java.util.*;
 
// Class
class GFG {
 
  // Main driver method
    public static void main(String[] args)
    {
      // Creating an ArrayList of Integer type
        ArrayList list = new ArrayList<>();
       
      // Adding elements to above object of Arrayist
      // Custom inputs
        list.add(20);
        list.add(4);
        list.add(76);
        list.add(21);
        list.add(3);
        list.add(80);
 
        var stream = list.stream();
 
        var numbers
            = stream.filter(number -> number % 2 == 0)
                  .filter(number -> number > 20);
       
      // Print all the elements of the stream on the console
        numbers.forEach(System.out::println);
    }
}

输出

76
80

Note: One can pass lambda also number -> System.out.println(number + ” “)