Java中的 Stream.concat()

Stream.concat() 方法创建一个连接流，其中元素是第一个流的所有元素，然后是第二个流的所有元素。如果两个输入流都是有序的，则结果流是有序的，如果任一输入流是并行的，则结果流是并行的。

句法：

static  Stream concat(Stream stream1, 
                            Stream stream2)

Where, T is the type of stream elements,
stream1 represents the first stream,
stream2 represents the second stream and
the function returns the concatenation of
the two input streams

对 Stream.concat(stream1, stream2) 的调用可以视为形成二叉树。所有输入流的串联位于根部。各个输入流位于叶子上。下面给出了最多四个输入流 a、b、c 和 d 的树的一些示例。

对于两个流 a 和 b，树看起来像：

对于三个流 a、b 和 c，树看起来像：

对于四个流 a、b、c 和 d，树看起来像：

每个额外的输入流都会为树增加一层深度，并增加一层间接层以到达所有其他流。

注意： Stream.concat() 方法返回的元素是有序的。例如，以下两行返回相同的结果：

Stream.concat(Stream.concat(stream1, stream2), stream3);
Stream.concat(stream1, Stream.concat(stream2, stream3));

但是下面两个的结果是不同的。

Stream.concat(Stream.concat(stream1, stream2), stream3); 
Stream.concat(Stream.concat(stream2, stream1), stream3);

下面是一些示例，可以更好地理解函数的实现。
示例 1：

// Implementation of Stream.concat()
// method in Java 8 with 2 Streams
import java.util.*;
import java.util.stream.IntStream;
import java.util.stream.Stream;
  
class GFG {
  
    // Driver code
    public static void main(String[] args)
    {
        // Creating two Streams
        Stream stream1 = Stream.of("Geeks", "for");
        Stream stream2 = Stream.of("GeeksQuiz", "GeeksforGeeks");
  
        // concatenating both the Streams
        // with Stream.concat() function
        // and displaying the result
        Stream.concat(stream1, stream2)
            .forEach(element -> System.out.println(element));
    }
}

输出：

Geeks
for
GeeksQuiz
GeeksforGeeks

示例 2：

// Implementation of Stream.concat()
// method in Java 8 with more than
// two Streams
import java.util.*;
import java.util.stream.IntStream;
import java.util.stream.Stream;
  
class GFG {
  
    // Driver code
    public static void main(String[] args)
    {
  
        // Creating more than two Streams
        Stream stream1 = Stream.of("Geeks");
        Stream stream2 = Stream.of("GeeksQuiz");
        Stream stream3 = Stream.of("GeeksforGeeks");
        Stream stream4 = Stream.of("GFG");
  
        // concatenating all the Streams
        // with Stream.concat() function
        // and displaying the result
        Stream.concat(Stream.concat(Stream.concat(stream1,
                             stream2), stream3), stream4)
            .forEach(element -> System.out.println(element));
    }
}

输出：

Geeks
GeeksQuiz
GeeksforGeeks
GFG

示例 3：

// Implementation of Stream.concat()
// method in Java 8 with DoubleStream
import java.util.*;
import java.util.stream.Stream;
import java.util.stream.DoubleStream;
  
class GFG {
  
    // Driver code
    public static void main(String[] args)
    {
  
        // Creating two Streams
        DoubleStream Stream1 = DoubleStream.of(1520, 1620);
        DoubleStream Stream2 = DoubleStream.of(1720, 1820);
  
        // concatenating both the Streams and
        // displaying the result
        DoubleStream.concat(Stream1, Stream2)
            .forEach(element -> System.out.println(element));
    }
}

输出：

示例 4：

// Implementation of Stream.concat()
// method in Java 8 and removing
// the duplicates
import java.util.*;
import java.util.stream.IntStream;
import java.util.stream.Stream;
  
class GFG {
  
    // Driver code
    public static void main(String[] args)
    {
  
        // Creating two Streams
        Stream stream1 = Stream.of("Geeks", "for", "GeeksforGeeks");
        Stream stream2 = Stream.of("GeeksQuiz", "GeeksforGeeks", "for");
  
        // concatenating both the Streams
        // with Stream.concat() function
        // and displaying the result after
        // removing the duplicates
        Stream.concat(stream1, stream2).distinct().forEach(element -> System.out.println(element));
    }
}

输出：

Geeks
for
GeeksforGeeks
GeeksQuiz

示例 5：

// Implementation of Stream.concat()
// method in Java 8 with LongStream
import java.util.*;
import java.util.stream.Stream;
import java.util.stream.LongStream;
  
class GFG {
  
    // Driver code
    public static void main(String[] args)
    {
  
        // Creating two Streams
        LongStream Stream1 = LongStream.of(1520, 1620);
        LongStream Stream2 = LongStream.of(1720, 1820);
  
        // concatenating both the Streams and
        // displaying the result
        LongStream.concat(Stream1, Stream2)
            .forEach(element -> System.out.println(element));
    }
}

输出：