Java 中的 Stream.concat()
Stream.concat()方法创建一个串联流，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，则结果流是有序的；如果两个输入流都是并行的，则并行。
语法:
static <T> Stream<T> concat(Stream<? extends T> stream1,
Stream<? extends T> 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)的调用可以看作是形成了一个二叉树。所有输入流的连接是在根。单个输入流在叶子上。下面给出了四个输入流 a、b、c 和 d 的树的一些例子。
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:
每个额外的输入流给树增加一层深度和一层间接到达所有其他流。
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);
下面是一些例子，可以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));
}
}
Output:
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));
}
}
Output:
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));
}
}
Output:
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));
}
}
Output:
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));
}
}
Output:
1520
1620
1720
1820
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