Java Stream.concat()

Stream.concat()方法创建一个连接的流，其中的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，那么生成的流就是有序的，如果其中一个输入流是平行的，那么生成的流就是平行的。

语法:

static <T> Stream<T> concat(Stream<? extends T > stream1, 
                            Stream<? extends T > stream2)

其中，T是流元素的类型。
stream1代表第一个流。
stream2代表第二个流，并且
该函数返回两个输入流的连接值
两个输入流的连接

对Stream.concat(stream1, stream2)的调用可以被认为是形成了一棵二进制树。所有输入流的串联在根部。单独的输入流在叶子上。下面给出了一些树的例子，最多有四个输入流a、b、c和d。

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：

每增加一个输入流就增加一层树的深度和一层指示，以达到所有其他的流。

注意： Stream.concat()方法返回的元素是有序的。例如，下面两行返回相同的结果。

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

但下面两个人的结果是不同的。

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

下面是一些例子，以便更好地理解函数的实现。
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<String> stream1 = Stream.of("Geeks", "for");
        Stream<String> 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

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<String> stream1 = Stream.of("Geeks");
        Stream<String> stream2 = Stream.of("GeeksQuiz");
        Stream<String> stream3 = Stream.of("GeeksforGeeks");
        Stream<String> 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

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:

1520.0
1620.0
1720.0
1820.0

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<String> stream1 = Stream.of("Geeks", "for", "GeeksforGeeks");
        Stream<String> 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

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:

1520
1620
1720
1820