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BAEL-6435: Reverse a String in Java 8 using Lambda and Streams (#13910)

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This commit is contained in:
Azhwani 2023-05-02 08:29:16 +02:00 committed by GitHub
parent 18834b349e
commit 7d86466fb7
2 changed files with 78 additions and 8 deletions
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38
core-java-modules/core-java-string-algorithms/src/main/java/com/baeldung/reverse/ReverseStringExamples.java
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@ -1,5 +1,9 @@
package com.baeldung.reverse;
import java.util.stream.Collectors;
import java.util.stream.IntStream;
import java.util.stream.Stream;
import org.apache.commons.lang3.StringUtils;
public class ReverseStringExamples {
@ -46,11 +50,43 @@ public class ReverseStringExamples {
}
return output.toString()
.trim();
.trim();
}
public static String reverseTheOrderOfWordsUsingApacheCommons(String sentence) {
return StringUtils.reverseDelimited(sentence, ' ');
}
public static String reverseUsingIntStreamRangeMethod(String str) {
if (str == null) {
return null;
}
char[] charArray = str.toCharArray();
return IntStream.range(0, str.length())
.mapToObj(i -> charArray[str.length() - i - 1])
.collect(StringBuilder::new, StringBuilder::append, StringBuilder::append)
.toString();
}
public static String reverseUsingStreamOfMethod(String str) {
if (str == null) {
return null;
}
return Stream.of(str)
.map(string -> new StringBuilder(string).reverse())
.collect(Collectors.joining());
}
public static String reverseUsingCharsMethod(String str) {
if (str == null) {
return null;
}
return str.chars()
.mapToObj(c -> (char) c)
.reduce("", (a, b) -> b + a, (a2, b2) -> b2 + a2);
}
}

48
core-java-modules/core-java-string-algorithms/src/test/java/com/baeldung/reverse/ReverseStringExamplesUnitTest.java
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@ -1,10 +1,11 @@
package com.baeldung.reverse;
import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertNull;
import org.apache.commons.lang3.StringUtils;
import org.junit.Test;
import static org.junit.Assert.assertEquals;
public class ReverseStringExamplesUnitTest {
private static final String STRING_INPUT = "cat";
@ -19,7 +20,7 @@ public class ReverseStringExamplesUnitTest {
String reversedEmpty = ReverseStringExamples.reverse(StringUtils.EMPTY);
assertEquals(STRING_INPUT_REVERSED, reversed);
assertEquals(null, reversedNull);
assertNull(reversedNull);
assertEquals(StringUtils.EMPTY, reversedEmpty);
}
@ -30,7 +31,7 @@ public class ReverseStringExamplesUnitTest {
String reversedEmpty = ReverseStringExamples.reverseUsingStringBuilder(StringUtils.EMPTY);
assertEquals(STRING_INPUT_REVERSED, reversed);
assertEquals(null, reversedNull);
assertNull(reversedNull);
assertEquals(StringUtils.EMPTY, reversedEmpty);
}
@ -41,7 +42,7 @@ public class ReverseStringExamplesUnitTest {
String reversedEmpty = ReverseStringExamples.reverseUsingApacheCommons(StringUtils.EMPTY);
assertEquals(STRING_INPUT_REVERSED, reversed);
assertEquals(null, reversedNull);
assertNull(reversedNull);
assertEquals(StringUtils.EMPTY, reversedEmpty);
}
@ -52,7 +53,7 @@ public class ReverseStringExamplesUnitTest {
String reversedEmpty = ReverseStringExamples.reverseTheOrderOfWords(StringUtils.EMPTY);
assertEquals(REVERSED_WORDS_SENTENCE, reversed);
assertEquals(null, reversedNull);
assertNull(reversedNull);
assertEquals(StringUtils.EMPTY, reversedEmpty);
}
@ -63,7 +64,40 @@ public class ReverseStringExamplesUnitTest {
String reversedEmpty = ReverseStringExamples.reverseTheOrderOfWordsUsingApacheCommons(StringUtils.EMPTY);
assertEquals(REVERSED_WORDS_SENTENCE, reversed);
assertEquals(null, reversedNull);
assertNull(reversedNull);
assertEquals(StringUtils.EMPTY, reversedEmpty);
}
@Test
public void whenReverseStringUsingIntStreamRangeMethod_ThenCorrectStringIsReturned() {
String reversed = ReverseStringExamples.reverseUsingIntStreamRangeMethod(STRING_INPUT);
String reversedNull = ReverseStringExamples.reverseUsingIntStreamRangeMethod(null);
String reversedEmpty = ReverseStringExamples.reverseUsingIntStreamRangeMethod(StringUtils.EMPTY);
assertEquals(STRING_INPUT_REVERSED, reversed);
assertNull(reversedNull);
assertEquals(StringUtils.EMPTY, reversedEmpty);
}
@Test
public void whenReverseStringUsingCharsMethod_ThenCorrectStringIsReturned() {
String reversed = ReverseStringExamples.reverseUsingCharsMethod(STRING_INPUT);
String reversedNull = ReverseStringExamples.reverseUsingCharsMethod(null);
String reversedEmpty = ReverseStringExamples.reverseUsingCharsMethod(StringUtils.EMPTY);
assertEquals(STRING_INPUT_REVERSED, reversed);
assertNull(reversedNull);
assertEquals(StringUtils.EMPTY, reversedEmpty);
}
@Test
public void whenReverseStringUsingStreamOfMethod_ThenCorrectStringIsReturned() {
String reversed = ReverseStringExamples.reverseUsingStreamOfMethod(STRING_INPUT);
String reversedNull = ReverseStringExamples.reverseUsingStreamOfMethod(null);
String reversedEmpty = ReverseStringExamples.reverseUsingStreamOfMethod(StringUtils.EMPTY);
assertEquals(STRING_INPUT_REVERSED, reversed);
assertNull(reversedNull);
assertEquals(StringUtils.EMPTY, reversedEmpty);
}