java-tutorials/java-strings/src/test/java/com/baeldung/string/StringToCharStreamUnitTest.java

package com.baeldung.string;

import org.junit.Test;

import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;
import java.util.stream.IntStream;
import java.util.stream.Stream;

import static org.hamcrest.CoreMatchers.instanceOf;
import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertNotNull;
import static org.junit.Assert.assertThat;

public class StringToCharStreamUnitTest {

    private String testString = "Tests";

    @Test
    public void givenTestString_whenChars_thenReturnIntStream() {
        assertThat(testString.chars(), instanceOf(IntStream.class));
    }

    @Test
    public void givenTestString_whenCodePoints_thenReturnIntStream() {
        assertThat(testString.codePoints(), instanceOf(IntStream.class));
    }

    @Test
    public void givenTestString_whenCodePoints_thenShowOccurences() throws Exception {
        Map<Character, Integer> map = testString.codePoints()
          .mapToObj(c -> (char) c)
          .filter(Character::isLetter)
          .collect(Collectors.toMap(c -> c, c -> 1, Integer::sum));

        System.out.println(map);
    }

    @Test
    public void givenIntStream_whenMapToObj_thenReturnCharacterStream() {
        Stream<Character> characterStream = testString.chars()
          .mapToObj(c -> (char) c);
        Stream<Character> characterStream1 = testString.codePoints()
          .mapToObj(c -> (char) c);
        assertNotNull("IntStream returned by chars() did not map to Stream<Character>", characterStream);
        assertNotNull("IntStream returned by codePoints() did not map to Stream<Character>", characterStream1);
    }

    @Test
    public void givenIntStream_whenMapToObj_thenReturnStringStream() {
        List<String> strings = testString.codePoints()
          .mapToObj(c -> String.valueOf((char) c))
          .collect(Collectors.toList());

        assertEquals(strings.size(), 5);
    }

}