[BAEL-3348] Moved code to algorithm-4

java-collections-maps/src/main/java/com/baeldung/map/MapUtil.java

@@ -0,0 +1,44 @@
+/**
+ * 
+ */
+package com.baeldung.map;
+
+import java.util.HashSet;
+import java.util.Map;
+import java.util.Map.Entry;
+import java.util.Set;
+import java.util.stream.Stream;
+
+/**
+ * @author swpraman
+ *
+ */
+public class MapUtil {
+    
+    public static <K, V> Stream<K> keys(Map<K, V> map, V value) {
+        return map.entrySet()
+                .stream()
+                .filter(entry -> value.equals(entry.getValue()))
+                .map(Map.Entry::getKey);
+    }
+    
+    public static <K, V> Set<K> getKeys(Map<K, V> map, V value) {
+        Set<K> keys = new HashSet<>();
+        for (Entry<K, V> entry : map.entrySet()) {
+            if (entry.getValue().equals(value)) {
+                keys.add(entry.getKey());
+            }
+        }
+        return keys;
+    }
+    
+    public static <K, V> K getKey(Map<K, V> map, V value) {
+        for (Entry<K, V> entry : map.entrySet()) {
+            if (entry.getValue().equals(value)) {
+                return entry.getKey();
+            }
+        }
+        return null;
+    }
+
+}

java-collections-maps/src/main/java/com/baeldung/map/MyKey.java

@@ -0,0 +1,64 @@
+package com.baeldung.map;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class MyKey {
+    private static final Logger LOG = LoggerFactory.getLogger(MyKey.class);
+    
+    private String name;
+    private int id;
+
+    public MyKey(int id, String name) {
+        this.id = id;
+        this.name = name;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    public int getId() {
+        return id;
+    }
+
+    public void setId(int id) {
+        this.id = id;
+    }
+
+    @Override
+    public int hashCode() {
+        LOG.debug("Calling hashCode()");
+        return id;
+    }
+
+    @Override
+    public String toString() {
+        return "MyKey [name=" + name + ", id=" + id + "]";
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+        LOG.debug("Calling equals() for key: " + obj);
+        if (this == obj)
+            return true;
+        if (obj == null)
+            return false;
+        if (getClass() != obj.getClass())
+            return false;
+        MyKey other = (MyKey) obj;
+        if (id != other.id)
+            return false;
+        if (name == null) {
+            if (other.name != null)
+                return false;
+        } else if (!name.equals(other.name))
+            return false;
+        return true;
+    }
+
+}

java-collections-maps/src/main/java/com/baeldung/map/MyLinkedHashMap.java

@@ -0,0 +1,23 @@
+package com.baeldung.map;
+
+import java.util.LinkedHashMap;
+import java.util.Map;
+
+public class MyLinkedHashMap<K, V> extends LinkedHashMap<K, V> {
+
+    /**
+     * 
+     */
+    private static final long serialVersionUID = 1L;
+    private static final int MAX_ENTRIES = 5;
+
+    public MyLinkedHashMap(int initialCapacity, float loadFactor, boolean accessOrder) {
+        super(initialCapacity, loadFactor, accessOrder);
+    }
+
+    @Override
+    protected boolean removeEldestEntry(Map.Entry eldest) {
+        return size() > MAX_ENTRIES;
+    }
+
+}