How to get Stream stream from collections and arrays in Java

Java gets Stream stream from collections and arrays

During the Java programming process,StreamStreams are an important tool for processing data structures such as collections and arrays, and they provide efficient and concise operation methods.

This article will introduce in detail how to obtain data structures such as collections and arrays.Streamflow.

1. Get Stream from the collection

Java'sCollectionThe interface provides us with direct accessStreamMethod:

method

stream(): Get a sequential stream.
parallelStream(): Get a parallel stream.

Sample code

import .*;
import .*;

public class Main {
    public static void main(String[] args) {
        // Create a collection        List&lt;String&gt; list = ("A", "B", "C");

        // Get sequential stream        Stream&lt;String&gt; stream = ();
        (::println);

        // Get parallel streams        Stream&lt;String&gt; parallelStream = ();
        (::println);
    }
}

Output result:

A
B
C

2. Get Stream from the array

ArraysThe class provides static methodsstream()Used to generate streams from arrays.

method

(T[] array): Convert the entire array into a sequential stream.
(T[] array, int startInclusive, int endExclusive): Convert part of the range of the array to a stream.

Sample code

import .*;
import .*;

public class Main {
    public static void main(String[] args) {
        // Create an array        String[] array = { "A", "B", "C", "D" };

        // Convert the entire array to a stream        Stream&lt;String&gt; stream = (array);
        (::println);

        // Convert partial range of array to stream        Stream&lt;String&gt; partialStream = (array, 1, 3);
        (::println); // Output B, C    }
}

Output result:

A
B
C
D
B
C

3. Use Get Stream

StreamThe interface provides static methods(), you can generate streams directly from elements or arrays.

Sample code

import .*;

public class Main {
    public static void main(String[] args) {
        // Use to generate streams from elements        Stream&lt;String&gt; stream = ("A", "B", "C");
        (::println);

        // Use to generate streams from array        String[] array = { "X", "Y", "Z" };
        Stream&lt;String&gt; arrayStream = (array);
        (::println);
    }
}

Output result:

A
B
C
X
Y
Z

4. Get Stream from the primitive type array

For basic type arrays (e.g.int[]、double[]), a specialized stream method can be used to generate a stream.

method

(int... values)
(double... values)
(int[] array)

Sample code

import .*;

public class Main {
    public static void main(String[] args) {
        // use        IntStream intStream = (1, 2, 3, 4);
        (::println);

        // use        int[] intArray = { 5, 6, 7, 8 };
        IntStream arrayStream = (intArray);
        (::println);
    }
}

Output result:

1
2
3
4
5
6
7
8

5. Get Stream from Map

MapNot belongingCollectionSubclass of the interface, so it cannot be called directlystream()method.

We can passentrySet()、keySet()orvalues()Indirectly obtaining the stream.

Sample code

import .*;
import .*;

public class Main {
    public static void main(String[] args) {
        // Create Map        Map&lt;String, Integer&gt; map = new HashMap&lt;&gt;();
        ("A", 1);
        ("B", 2);
        ("C", 3);

        // Get key stream        Stream&lt;String&gt; keyStream = ().stream();
        (::println);

        // Get the value stream        Stream&lt;Integer&gt; valueStream = ().stream();
        (::println);

        // Get key-value convection        Stream&lt;&lt;String, Integer&gt;&gt; entryStream = ().stream();
        (entry -&gt; (() + ": " + ()));
    }
}

Output result:

A
B
C
1
2
3
A: 1
B: 2
C: 3

Summarize

Data Type	method
gather	stream() or parallelStream()
Array	() or ()
Basic type array	() or ()
Map	Use entrySet(), keySet(), values()

The above is personal experience. I hope you can give you a reference and I hope you can support me more.