pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>ru.yandex.shad</groupId>
    <artifactId>shad-reader</artifactId>
    <version>1.0-SNAPSHOT</version>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.hamcrest</groupId>
            <artifactId>hamcrest-all</artifactId>
            <version>1.3</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>com.github.stefanbirkner</groupId>
            <artifactId>system-rules</artifactId>
            <version>1.13.0</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>pl.pragmatists</groupId>
            <artifactId>JUnitParams</artifactId>
            <version>1.0.4</version>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.1</version>
                <configuration>
                    <source>${java.version}</source>
                    <target>${java.version}</target>
                </configuration>
            </plugin>
        </plugins>
    </build>

</project>

ShadReader.java

import java.io.BufferedReader;
import java.io.Closeable;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.NoSuchElementException;

public class ShadReader implements Closeable {
    private static final int BUFFER_SIZE = 1024;

    private final BufferedReader source;
    private int currentCodePoint = ' ';

    public ShadReader(InputStream stream) {
        source = new BufferedReader(new InputStreamReader(stream), BUFFER_SIZE);
    }

    @Override
    public void close() throws IOException {
        source.close();
    }

    public boolean hasNext() {
        return hasNextNonWhitespaceSymbol();
    }

    public int nextInt() {
        return Integer.parseInt(nextToken());
    }

    public long nextLong() {
        return Long.parseLong(nextToken());
    }

    public double nextDouble() {
        return Double.parseDouble(nextToken());
    }

    public String nextToken() {
        if (!hasNext()) {
            throw new NoSuchElementException("Input is already exhausted.");
        }

        StringBuilder token = new StringBuilder();

        do {
            token.appendCodePoint(currentCodePoint);
            advance();
        } while (isNotEndOfFile() && !isWhitespace());

        return token.toString();
    }

    private boolean hasNextNonWhitespaceSymbol() {
        while (isNotEndOfFile() && isWhitespace()) {
            advance();
        }

        return isNotEndOfFile() && !isWhitespace();
    }

    private void advance() {
        try {
            currentCodePoint = source.read();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    private boolean isWhitespace() {
        return Character.isWhitespace(currentCodePoint);
    }

    private boolean isNotEndOfFile() {
        return currentCodePoint != -1;
    }

}

ShadReaderTest.java

import junitparams.JUnitParamsRunner;
import junitparams.Parameters;
import org.junit.After;
import org.junit.Rule;
import org.junit.Test;
import org.junit.contrib.java.lang.system.TextFromStandardInputStream;
import org.junit.runner.RunWith;

import java.io.IOException;
import java.util.NoSuchElementException;

import static org.hamcrest.Matchers.is;
import static org.junit.Assert.assertThat;

@RunWith(JUnitParamsRunner.class)
public class ShadReaderTest {
    private ShadReader reader;

    @Rule
    public TextFromStandardInputStream systemIn =
            TextFromStandardInputStream.emptyStandardInputStream();

    @Test
    @Parameters(method = "notBlankStrings")
    public void itShouldHasNext(String text) {
        systemIn.provideText(text);

        reader = new ShadReader(System.in);

        assertThat(reader.hasNext(), is(true));
    }

    private Object[][] notBlankStrings() {
        return new Object[][]{
                {"apple"},
                {" banana "},
                {" \t \r\n pear \n  \t"},
                {" \r\npeach\t\n "},
                {"\t 12345678901234567890 \r\n "}
        };
    }

    @Test
    @Parameters(method = "blankStrings")
    public void itShouldNotHaveNext(String text) {
        systemIn.provideText(text);

        reader = new ShadReader(System.in);

        assertThat(reader.hasNext(), is(false));
    }

    @Test(expected = NoSuchElementException.class)
    @Parameters(method = "blankStrings")
    public void itShouldThrowNoSuchElementExceptionOnBlankInput(String text) {
        systemIn.provideText(text);

        reader = new ShadReader(System.in);

        reader.nextToken();
    }

    private Object[][] blankStrings() {
        return new Object[][]{
                {""},
                {" \t "},
                {" \t \r\n  \n  \t"},
                {" \r\n \t\n "},
                {"\t  \r\n "}
        };
    }

    @Test
    @Parameters(method = "notBlankStrings,blankStrings")
    public void hasNextShouldBeIdempotent(String text) {
        systemIn.provideText(text);

        reader = new ShadReader(System.in);

        assertThat(reader.hasNext(), is(reader.hasNext()));
    }

    @Test
    @Parameters(method = "tokens")
    public void itShouldReadNextToken(String text, String token) {
        systemIn.provideText(text);

        reader = new ShadReader(System.in);

        assertThat(reader.nextToken(), is(token));
    }

    private Object[][] tokens() {
        return new Object[][]{
                {"apple", "apple"},
                {" banana ", "banana"},
                {" \t \r\n pear \n  \t", "pear"},
                {" \r\npeach\t\n ", "peach"},
                {"\t 12345678901234567890 \r\n ", "12345678901234567890"}
        };
    }

    @Test
    @Parameters(method = "ints")
    public void itShouldReadNextInt(String text, int number) {
        systemIn.provideText(text);

        reader = new ShadReader(System.in);

        assertThat(reader.nextInt(), is(number));
    }

    private Object[][] ints() {
        return new Object[][]{
                {"1", 1},
                {" 0 ", 0},
                {" \t \r\n 12345 \r\n  \t", 12345},
                {" \r\n-567890 \n ", -567890},
                {" \n+5 ", 5}
        };
    }

    @Test
    @Parameters(method = "longs")
    public void itShouldReadNextLong(String text, long number) {
        systemIn.provideText(text);

        reader = new ShadReader(System.in);

        assertThat(reader.nextLong(), is(number));
    }

    private Object[][] longs() {
        return new Object[][]{
                {"1", 1L},
                {" 0 ", 0L},
                {" \t \r\n 9876543210 \n  \t", 9876543210L},
                {" \n-1234567890\r\n", -1234567890L},
                {" \r\n+5 ", 5L}
        };
    }

    @Test
    @Parameters(method = "doubles")
    public void itShouldReadNextDouble(String text, double number) {
        systemIn.provideText(text);

        reader = new ShadReader(System.in);

        assertThat(reader.nextDouble(), is(number));
    }

    private Object[][] doubles() {
        return new Object[][]{
                {"1", 1D},
                {" 0 ", 0D},
                {" \t \r\n 9876543210 \n  \t", 9876543210D},
                {" \n-1234567890\r\n", -1234567890D},
                {" \r\n+5 ", 5D},
                {" \r\n1.2345678E7 ", 1.2345678E7},
                {" \r\n -1.2345678E-7 \t", -1.2345678E-7},
        };
    }

    @Test
    public void itShouldReadDataSequence() {
        systemIn.provideText(" \t apple   \r\n \t123 \n   2.0 \n 567 \t \n ");

        reader = new ShadReader(System.in);

        assertThat(reader.nextToken(), is("apple"));
        assertThat(reader.nextInt(), is(123));
        assertThat(reader.nextDouble(), is(2D));
        assertThat(reader.nextLong(), is(567L));
    }

    @After
    public void tearDown() throws IOException {
        reader.close();
    }

}