[appB] Examples for lambdas and maps (6c5b2d99) · Commits · examples / Head First Java 3rd Edition

src/main/java/appB/MapMethods.java

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Changes for src/main/java/appB/MapMethods.java: 41 added lines, 0 removed lines.
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		package appB;

		import java.util.HashMap;
		import java.util.Map;

		public class MapMethods {
		void addOrGetCustomer(String usr) {
		Map<String, Actions> custActs = new HashMap<>();
		Actions actions = custActs.computeIfAbsent(usr, name -> new Actions(name));
		// do something with activity
		}

		void addOrGetCustomerOld(String usr) {
		Map<String, Actions> custActs = new HashMap<>();
		// probably other stuff happens here...
		Actions actions = custActs.get(usr);
		if (actions == null) {
		actions = new Actions(usr);
		custActs.put(usr, actions);
		}
		// do something with actions
		}

		void incrementMetricWeCareAbout(String metric) {
		Map<String, Integer> metrics = new HashMap<>();
		// probably other stuff happens here...

		if (metrics.containsKey(metric)) {
		Integer integer = metrics.get(metric);
		metrics.put(metric, ++integer);
		}
		}

		private class Actions {
		private String username;

		public Actions(String username) {
		this.username = username;
		}
		}
		}

src/test/java/appB/MapMethodsTest.java

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Changes for src/test/java/appB/MapMethodsTest.java: 69 added lines, 0 removed lines.
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		package appB;

		import org.junit.jupiter.api.Assertions;
		import org.junit.jupiter.api.Test;

		import java.util.HashMap;
		import java.util.Map;

		class MapMethodsTest {

		@Test
		void shouldOnlyAddMetricsThatWeCareAbout() {
		Map<String, Integer> metrics = new HashMap<>();
		metrics.put("metric 1", 0);
		metrics.put("metric 2", 0);
		metrics.put("metric 3", 0);

		Integer newValue = metrics.computeIfPresent("metric 1", (key, value) -> ++value);
		System.out.println("metrics = " + metrics);
		Assertions.assertEquals(1, metrics.get("metric 1"));
		Assertions.assertEquals(1, newValue);

		metrics.computeIfPresent("metric 4", (s, integer) -> ++integer);
		System.out.println("metrics = " + metrics);
		Assertions.assertFalse(metrics.containsKey("metric 4"));
		}

		@Test
		void shouldOnlyAddMetricsThatWeCareAboutOld() {
		Map<String, Integer> metrics = new HashMap<>();
		metrics.put("metric 1", 0);
		metrics.put("metric 2", 0);
		metrics.put("metric 3", 0);

		String key = "metric 1";
		if (metrics.containsKey(key)) {
		Integer value = metrics.get(key);
		metrics.put(key, ++value);
		}
		System.out.println("metrics = " + metrics);
		Assertions.assertEquals(1, metrics.get("metric 1"));
		}

		@Test
		void shouldSeeWhatReplaceAllLooksLike() {
		Map<String, Integer> metrics = new HashMap<>();
		metrics.put("metric 1", 0);
		metrics.put("metric 2", 0);
		metrics.put("metric 3", 0);

		metrics.replaceAll((key, value) -> ++value);
		Assertions.assertEquals(1, metrics.get("metric 1"));
		Assertions.assertEquals(1, metrics.get("metric 2"));
		Assertions.assertEquals(1, metrics.get("metric 3"));
		}

		@Test
		void shouldSeeWhatForEachLooksLike() {
		Map<String, Integer> metrics = new HashMap<>();
		metrics.put("metric 1", 0);
		metrics.put("metric 2", 0);
		metrics.put("metric 3", 0);

		metrics.forEach((key, value) -> {
		System.out.println("key = " + key);
		System.out.println("value = " + value);
		});
		}
		}
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