The BaseStream interface. Examples of using interface methods

Before studying this topic, it is recommended that you familiarize yourself with the following topic:

• Data streams. Stream API. General information

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Contents

• 1. List of methods of the BaseStream interface
• 2. Method close(). Closing the data stream. Example
• 3. Method isParallel(). Determining if the data stream is parallel. Example
• 4. Method iterator(). Get the iterator for data stream. Example
• 5. Method onClose(). Get the stream with the specified close event handler. Example
• 6. Method parallel(). Return the parallel data stream. Example
• 7. Method sequential(). Return a sequential data stream. Example
• 8. Method unordered(). Return the unordered data stream. Example
• Related topics

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1. List of methods of the BaseStream interface

Below is a list of the main methods of the BaseStream interface and their purpose:

• close() – close data stream;
• isParallel() – determine if a stream is parallel;
• iterator() – get an iterator for a stream;
• onClose() – set the stream close event handler;
• parallel() – return parallel data stream;
• sequential() – return sequential data stream;
• spliterator() – get an iterator-delimiter;
• unordered() – return an unordered data stream.

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2. Method close(). Closing the data stream. Example

To close the data stream, the close() method is used, which has the following general form

void close();

Be sure to close only those data streams that are associated with files. Closing other data streams is optional.

The example demonstrates how to close the System.in data stream that follows from keyboard input. The Scanner class is used to enter data. First, an array of integers is formed, then this array is displayed. At the end of the program, the data stream is closed by the close() method.

// Examples of opening/closing a data stream
import java.util.stream.*;
import java.util.*;

public class TrainStreamAPI {

  public static void main(String[] args) {
    // Method close()
    // Get data stream from keyboard
    Scanner scanner = new Scanner(System.in);

    // Read the array of numbers. End of input - number 0
    Integer num;
    ArrayList<Integer> AL = new ArrayList();

    while (true) {
      System.out.print("num = ");

      // Get number from keyboard
      num = scanner.nextInt();

      // Check if 0 is entered
      if (num==0) break;

      // Add number to array
      AL.add(num);
    }

    // Display array to screen
    System.out.println("End of input.");
    System.out.println("AL = " + AL);

    // Close the stream
    scanner.close();
  }
}

Program execution result

num = 15
num = 18
num = -9
num = 3
num = 0
End of input.
AL = [15, 18, -9, 3]

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3. Method isParallel(). Determining if the data stream is parallel. Example

The isParallel() method is designed to determine if the calling data stream is parallel. The method has the following general form:

boolean isParallel()

The method returns true if the data stream is parallel. If the data stream is sequential, then the method returns false.

The text of the program demonstrating the use of the isParallel() method is as follows.

import java.util.ArrayList;
import java.util.stream.*;

public class StreamAPI {

  public static void main(String[] args) {
    // The IsParallel() method - determine if data stream is parallel

    // 1. Create an array of numbers that will be a data stream
    ArrayList<Integer> AL = new ArrayList<Integer>();
    for (int i=0; i<10; i++) {
      AL.add((int)(Math.random()*100)); // numbers from 0 to 99
    }

    // 2. Display the array
    System.out.println(AL);

    // 3. Get serial data stream from AL array
    Stream<Integer> stream = AL.stream();

    // 4. Determine if stream is parallel
    if (stream.isParallel())
      System.out.println("stream is parallel");
    else 
      System.out.println("stream is not parallel");

    // 5. Get parallel data stream from AL array
    Stream<Integer> parallelStream = AL.parallelStream();

    // 6. Determine if parallelStream is parallel
    if (parallelStream.isParallel())
      System.out.println("parallelStream is parallel");
    else
      System.out.println("parallelStream is not parallel");
  }
}

Program execution result

[48, 64, 30, 40, 19, 17, 27, 75, 48, 52]
stream is not parallel
parallelStream is parallel

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4. Method iterator(). Get the iterator for data stream. Example

The iterator() method is for getting an iterator. Using iterator, you can view and process the elements of a stream. The general form of the method is as follows

Iterator<T> iterator()

here

• Iterator<T> – a type that characterizes an iterator that processes elements of some generic type T.

The method is the final operation.

The text of the program, demonstrating the iterator() method, are shown below.

import java.util.*;
import java.util.stream.*;
import java.util.function.*;

public class StreamAPI {

  public static void main(String[] args) {
    // 1. Create a set of numbers
    ArrayList<Double> AL = new ArrayList<Double>();
    AL.add(1.5);
    AL.add(2.8);
    AL.add(-2.3);
    AL.add(3.4);
    AL.add(1.1);

    // 2. Create a stream of data from a set of numbers AL
    Stream<Double> stream = AL.stream();

    // 3. Get an iterator for stream
    Iterator<Double> it = stream.iterator();

    // 4. Display elements of a stream using an iterator
    System.out.print("stream = ");
    while (it.hasNext()) {
      System.out.print(it.next()+" ");
    }
    System.out.println();

    // 5. Remove negative stream elements, create resulting array
    ArrayList<Double> AL2 = new ArrayList<Double>();
    double t;

    // Form a new stream and get an iterator on it
    stream = AL.stream();
    it = stream.iterator();

    // Loop through stream
    while (it.hasNext()) {
      // Get a number from stream
      t = it.next();

      // If the number is positive, then add it to the array AL2
      if (t>=0.0)
        AL2.add(t);
    }

    // 6. Display array AL2
    System.out.println("AL2 = " + AL2);
  }
}

Program execution result

stream = 1.5 2.8 -2.3 3.4 1.1
AL2 = [1.5, 2.8, 3.4, 1.1]

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5. Method onClose(). Get the stream with the specified close event handler. Example

The onClose() method allows you to set up a thread close event handler – a special method that will be called when the thread is closed and perform some finishing actions.

The onClose() method has the following general form

S onClose(Runnable closeHandler)

here

• closeHandler – the class that contains the run() method of the Runnable interface. The run() method contains the code that needs to be executed when the calling thread is closed;
• S – a stream with a closeHandler installed;

After the closeHandler has been set, it is called when the calling thread executes the close() method.

Example. The example declares the MyCloseStream class, which acts as a handler called when the stream is closed.

The MyCloseStream class implements the Runnable interface. This means that the class must implement a single run() method of the Runnable interface. The run() method contains the code that should be executed when the stream is closed. In the program, for demonstration purposes, a simple informational message is displayed in the run() method.

The demo program is as follows.

import java.util.*;
import java.util.stream.*;

// A class of stream closing event handler.
class MyCloseStream implements Runnable {

  // Method that closes the stream
  public void run() {
    // Here code, which is called when the stream is closed

    // Display some informational message
    System.out.println("Close the stream.");

    // ...
  }
}

public class StreamAPI {

  public static void main(String[] args) {
    // Demonstration of calling the run() method of the MyCloseStream class
    // 1. Create a set of numbers
    ArrayList<Integer> AL = new ArrayList<Integer>();
    AL.add(25);
    AL.add(31);
    AL.add(22);
    AL.add(18);
    AL.add(11);

    // 2. Create a data stream
    Stream<Integer> stream = AL.stream();

    // 3. Specify the handler close the stream
    MyCloseStream handler = new MyCloseStream();

    // 4. Call the onClose() method of stream
    // and pass it a handler - an instance of handler.
    stream.onClose(handler);

    // 5. Close stream:
    // the stream closing handler is called
    stream.close(); // Close the stream
  }
}

Program execution result

Close the stream.

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6. Method parallel(). Return the parallel data stream. Example

The parallel() method allows you to get a parallel stream from the calling stream. If the calling stream is already parallel, then this stream is returned. The parallel() method is an intermediate operation and has the following general form:

S parallel()

here

• S – the resulting parallel stream.

The text of the program, demonstrating the parallel() method is as follows:

import java.util.*;
import java.util.stream.*;

public class StreamAPI {

  public static void main(String[] args) {
    // 1. Create a set of numbers
    ArrayList<Integer> AL = new ArrayList<Integer>();
    AL.add(20);
    AL.add(32);
    AL.add(12);
    AL.add(23);
    AL.add(51);

    // 2. Create sequential data stream
    Stream<Integer> stream = AL.stream();

    // 3. Check if the stream is parallel
    if (stream.isParallel())
      System.out.println("stream is parallel");
    else
      System.out.println("stream is sequential");

    // 4. Call the parallel() method - form a parallel stream
    Stream<Integer> stream2 = stream.parallel();

    // 5. Display stream data
    if (stream2.isParallel())
      System.out.println("stream2 is parallel");
    else
      System.out.println("stream2 is sequential");
  }
}

Program execution result

stream is sequential
stream2 is parallel

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7. Method sequential(). Return a sequential data stream. Example

The sequential() method allows you to get a sequential stream from the calling stream. If the calling stream is sequential, the same stream is returned. The method is an intermediate operation. The method has the following general form:

S sequential()

here

• S – the resulting sequential stream.

The code of the program demonstrating the sequential() method is shown below.

import java.util.*;
import java.util.stream.*;

public class StreamAPI {

  public static void main(String[] args) {
    // 1. Create a set of numbers
    ArrayList<Integer> AL = new ArrayList<Integer>();
    AL.add(20);
    AL.add(32);
    AL.add(12);
    AL.add(23);
    AL.add(51);

    // 2. Create the sequential data stream
    Stream<Integer> stream = AL.stream();

    // 3. Check that the stream is sequential
    if (stream.isParallel())
      System.out.println("stream is parallel");
    else
      System.out.println("stream is sequential");

    // 4. Call the sequential() method - form a sequential stream
    Stream<Integer> stream2 = stream.sequential();

    // 5. Display data about stream2
    if (stream2.isParallel())
      System.out.println("stream2 is parallel");
    else
      System.out.println("stream2 is sequential");
  }
}

Program execution result

stream is sequential
stream2 is sequential

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8. Method unordered(). Return the unordered data stream. Example

The unordered() method returns an unordered data stream based on the calling stream. If the calling data stream is unordered, then this stream is returned.

The general form of the method is as follows:

S unordered()

here

• S – the resulting unordered stream.

The method is the intermediate operation.

The text of the program demonstrating the unordered() method is as follows.

import java.util.*;
import java.util.stream.*;
import java.util.function.*;

public class StreamAPI {

  public static void main(String[] args) {
    // 1. Create a set of numbers
    ArrayList<Double> AL = new ArrayList<Double>();
    AL.add(1.5);
    AL.add(2.8);
    AL.add(-2.3);
    AL.add(3.4);
    AL.add(1.1);

    // 2. Create data stream from set of AL numbers
    Stream<Double> stream = AL.stream();

    // 3. Sort stream
    stream = stream.sorted();

    // 4. Display the stream
    // 4.1. Declare an action that displays an element of type Double
    Consumer<Double> action = (n) -> {
      System.out.print(n + " ");
    };

    // 4.2. Invoke method forEach()
    System.out.print("Sorted Array AL = [");
    stream.forEach(action);
    System.out.println("]");

    // 5. Create a new unordered stream - the unordered() method
    stream = AL.stream().unordered();

    // 6. Display unordered stream
    System.out.print("Unordered Array AL = [");
    stream.forEach(action);
    System.out.println("]");
  }
}

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Related topics

• Data streams. Stream API. General information
• The concept of final and intermediate operations. Examples. Methods stream(), parallelStream()
• Interface Stream<T>. Intermediate interface methods: filter(), map(), mapToDouble(), mapToInt(), mapToLong(), sorted(). Examples
• Interface Stream<T>. Final methods collect(), count(), forEach(), max(), min(), reduce(), toArray()
• Examples of solving tasks on data streams
• Examples of solving tasks on data streams, which are objects of the developed classes

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