BAEL-6781: Skip First Iteration in Java Foreach (#14876)
This commit is contained in:
Eugene Kovko
GitHub
parent
d00863eeb2
commit
9e5c656d84
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package com.baeldung.skippingfirstelement;
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import java.util.ArrayList;
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import java.util.HashMap;
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import java.util.HashSet;
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import java.util.Iterator;
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import java.util.List;
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import java.util.Map;
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import java.util.Map.Entry;
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import java.util.Set;
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public class SkipFirstElementExample {
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private final List<String> stringList = new ArrayList<>();
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private final Set<String> stringSet = new HashSet<>();
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private final Map<String, String> stringMap = new HashMap<>();
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public SkipFirstElementExample() {
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// Initializing a List
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stringList.add("Monday");
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stringList.add("Tuesday");
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stringList.add("Wednesday");
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stringList.add("Thursday");
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stringList.add("Friday");
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stringList.add("Saturday");
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stringList.add("Sunday");
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// Initializing a Set
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stringSet.add("Monday");
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stringSet.add("Tuesday");
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stringSet.add("Wednesday");
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stringSet.add("Thursday");
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stringSet.add("Friday");
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stringSet.add("Saturday");
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stringSet.add("Sunday");
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// Initializing a Map
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stringMap.put("Monday", "The day when coffee is a life support system.");
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stringMap.put("Tuesday", "The day you realize that Monday's optimism was a lie.");
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stringMap.put("Wednesday", "Hump Day, or as it's known, the 'Is it Friday yet?' day.");
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stringMap.put("Thursday", "The day that says, 'Hold my beer, Friday is coming!'");
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stringMap.put("Friday", "The golden child of the weekdays. The superhero of the workweek.");
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stringMap.put("Saturday", "The day of rest? More like the day of 'What can I binge-watch next?'");
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stringMap.put("Sunday", "The day before you have to adult again.");
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}
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void skippingFirstElementInListWithForLoop(List<String> stringList) {
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for (int i = 1; i < stringList.size(); i++) {
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process(stringList.get(i));
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}
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}
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void skippingFirstElementInListWithWhileLoop(List<String> stringList) {
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final Iterator<String> iterator = stringList.iterator();
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if (iterator.hasNext()) {
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iterator.next();
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}
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while (iterator.hasNext()) {
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process(iterator.next());
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}
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}
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void skippingFirstElementInSetWithWhileLoop(Set<String> stringSet) {
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final Iterator<String> iterator = stringSet.iterator();
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if (iterator.hasNext()) {
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iterator.next();
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}
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while (iterator.hasNext()) {
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process(iterator.next());
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}
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}
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void skippingFirstElementInListWithWhileLoopStoringFirstElement(List<String> stringList) {
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final Iterator<String> iterator = stringList.iterator();
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String firstElement = null;
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if (iterator.hasNext()) {
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firstElement = iterator.next();
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}
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while (iterator.hasNext()) {
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process(iterator.next());
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// additional logic using fistElement
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}
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}
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void skippingFirstElementInMapWithStreamSkip(Map<String, String> stringMap) {
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stringMap.entrySet().stream().skip(1).forEach(this::process);
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}
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void skippingFirstElementInListWithSubList(List<String> stringList) {
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for (final String element : stringList.subList(1, stringList.size())) {
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process(element);
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}
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}
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void skippingFirstElementInListWithForLoopWithAdditionalCheck(List<String> stringList) {
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for (int i = 0; i < stringList.size(); i++) {
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if (i == 0) {
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// do something else
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} else {
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process(stringList.get(i));
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}
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}
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}
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void skippingFirstElementInListWithWhileLoopWithCounter(List<String> stringList) {
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int counter = 0;
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while (counter < stringList.size()) {
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if (counter != 0) {
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process(stringList.get(counter));
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}
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++counter;
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}
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}
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void skippingFirstElementInListWithReduce(List<String> stringList) {
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stringList.stream().reduce((skip, element) -> {
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process(element);
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return element;
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});
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}
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protected void process(String string) {
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System.out.println(string);
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}
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protected void process(Entry<String, String> mapEntry) {
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System.out.println(mapEntry);
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}
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}
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package com.baeldung.skippingfirstelement;
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import static org.junit.jupiter.api.Assertions.*;
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import java.util.HashSet;
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import java.util.List;
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import java.util.Map;
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import java.util.Set;
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import java.util.stream.Stream;
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import org.junit.jupiter.api.BeforeEach;
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import org.junit.jupiter.api.condition.EnabledForJreRange;
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import org.junit.jupiter.api.condition.JRE;
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import org.junit.jupiter.params.ParameterizedTest;
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import org.junit.jupiter.params.provider.Arguments;
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import org.junit.jupiter.params.provider.MethodSource;
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@EnabledForJreRange(min = JRE.JAVA_9)
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class SkipFirstElementExampleUnitTest {
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private static TestableSkipFirstElement testableSkip = new TestableSkipFirstElement();
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@BeforeEach
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void setup() {
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testableSkip.reset();
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}
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private static Stream<Arguments> listProvider() {
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return Stream.of(
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Arguments.of(
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List.of("Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday"),
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List.of("Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday"))
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);
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}
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private static Stream<Arguments> mapProvider() {
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return Stream.of(
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Arguments.of(
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Map.of(
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"Monday", "The day when coffee is a life support system.",
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"Tuesday", "The day you realize that Monday's optimism was a lie.",
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"Wednesday", "Hump Day, or as it's known, the 'Is it Friday yet?' day.",
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"Thursday", "The day that says, 'Hold my beer, Friday is coming!'",
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"Friday", "The golden child of the weekdays. The superhero of the workweek.",
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"Saturday", "The day of rest? More like the day of 'What can I binge-watch next?'",
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"Sunday", "The day before you have to adult again."
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)
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)
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);
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}
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@ParameterizedTest
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@MethodSource("listProvider")
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void skippingFirstElementInListWithForLoop(List<String> input, List<String> expected) {
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testableSkip.skippingFirstElementInListWithForLoop(input);
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List<?> actual = testableSkip.getResult();
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assertEquals(actual, expected);
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}
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@ParameterizedTest
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@MethodSource("listProvider")
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void skippingFirstElementInListWithWhileLoop(List<String> input, List<String> expected) {
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testableSkip.skippingFirstElementInListWithWhileLoop(input);
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List<?> actual = testableSkip.getResult();
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assertEquals(actual, expected);
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}
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@ParameterizedTest
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@MethodSource("listProvider")
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void skippingFirstElementInSetWithWhileLoop(List<String> input) {
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testableSkip.skippingFirstElementInSetWithWhileLoop(new HashSet<>(input));
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Set<?> actual = new HashSet<>(testableSkip.getResult());
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assertEquals(actual.size(), input.size() - 1);
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}
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@ParameterizedTest
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@MethodSource("listProvider")
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void skippingFirstElementInListWithWhileLoopStoringFirstElement(List<String> input, List<String> expected) {
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testableSkip.skippingFirstElementInListWithWhileLoopStoringFirstElement(input);
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List<?> actual = testableSkip.getResult();
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assertEquals(actual, expected);
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}
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@ParameterizedTest
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@MethodSource("mapProvider")
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void skippingFirstElementInMapWithStreamSkip(Map<String, String> input) {
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testableSkip.skippingFirstElementInMapWithStreamSkip(input);
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List<?> actual = testableSkip.getResult();
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assertEquals(actual.size(), input.size() - 1);
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}
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@ParameterizedTest
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@MethodSource("listProvider")
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void skippingFirstElementInListWithSubList(List<String> input, List<String> expected) {
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testableSkip.skippingFirstElementInListWithSubList(input);
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List<?> actual = testableSkip.getResult();
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assertEquals(actual, expected);
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}
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@ParameterizedTest
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@MethodSource("listProvider")
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void skippingFirstElementInListWithForLoopWithAdditionalCheck(List<String> input, List<String> expected) {
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testableSkip.skippingFirstElementInListWithForLoopWithAdditionalCheck(input);
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List<?> actual = testableSkip.getResult();
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assertEquals(actual, expected);
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}
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@ParameterizedTest
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@MethodSource("listProvider")
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void skippingFirstElementInListWithWhileLoopWithCounter(List<String> input, List<String> expected) {
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testableSkip.skippingFirstElementInListWithWhileLoopWithCounter(input);
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List<?> actual = testableSkip.getResult();
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assertEquals(actual, expected);
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}
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@ParameterizedTest
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@MethodSource("listProvider")
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void skippingFirstElementInListWithReduce(List<String> input, List<String> expected) {
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testableSkip.skippingFirstElementInListWithReduce(input);
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List<?> actual = testableSkip.getResult();
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assertEquals(actual, expected);
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}
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}
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package com.baeldung.skippingfirstelement;
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import java.util.List;
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public interface TestableSkip {
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void reset();
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List<?> getResult();
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}
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@ -0,0 +1,37 @@
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package com.baeldung.skippingfirstelement;
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import java.util.ArrayList;
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import java.util.List;
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import java.util.Map.Entry;
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public class TestableSkipFirstElement extends SkipFirstElementExample implements TestableSkip {
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private List<String> processedList = new ArrayList<>();
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private List<Entry<String, String>> processedEntryList = new ArrayList<>();
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@Override
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public void process(String string) {
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processedList.add(string);
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}
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@Override
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public void process(Entry<String, String> stringEntry) {
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processedEntryList.add(stringEntry);
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}
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@Override
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public void reset() {
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processedList.clear();
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processedEntryList.clear();
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}
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@Override
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public List<?> getResult() {
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if (!processedList.isEmpty())
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return processedList;
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return processedEntryList;
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}
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}
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