BAEL-4716 HashMap optimization (#10479)

java-collections-maps-3/src/main/java/com/baeldung/map/hashing/Member.java

@@ -0,0 +1,6 @@
+package com.baeldung.map.hashing;
+
+class Member {
+    Integer id;
+    String name;
+}

java-collections-maps-3/src/main/java/com/baeldung/map/hashing/MemberWithBadHashing.java

@@ -0,0 +1,8 @@
+package com.baeldung.map.hashing;
+
+public class MemberWithBadHashing extends Member {
+    @Override
+    public int hashCode() {
+        return name.hashCode();
+    }
+}

java-collections-maps-3/src/main/java/com/baeldung/map/hashing/MemberWithGuavaHashing.java

@@ -0,0 +1,18 @@
+package com.baeldung.map.hashing;
+
+import com.google.common.base.Charsets;
+import com.google.common.hash.HashFunction;
+import com.google.common.hash.Hashing;
+
+public class MemberWithGuavaHashing extends Member {
+    @Override
+    public int hashCode() {
+        HashFunction hashFunction = Hashing.murmur3_32();
+        return hashFunction.newHasher()
+                .putInt(id)
+                .putString(name, Charsets.UTF_8)
+                .hash().hashCode();
+    }
+
+
+}

java-collections-maps-3/src/main/java/com/baeldung/map/hashing/MemberWithId.java

@@ -0,0 +1,18 @@
+package com.baeldung.map.hashing;
+
+public class MemberWithId extends Member {
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) return true;
+        if (o == null || getClass() != o.getClass()) return false;
+
+        MemberWithId that = (MemberWithId) o;
+
+        return id.equals(that.id);
+    }
+
+    @Override
+    public int hashCode() {
+        return id;
+    }
+}

java-collections-maps-3/src/main/java/com/baeldung/map/hashing/MemberWithIdAndName.java

@@ -0,0 +1,23 @@
+package com.baeldung.map.hashing;
+
+import java.util.Objects;
+
+public class MemberWithIdAndName extends Member {
+    public static final int PRIME = 31;
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) return true;
+        if (o == null || getClass() != o.getClass()) return false;
+        MemberWithObjects that = (MemberWithObjects) o;
+        return Objects.equals(id, that.id) &&
+                Objects.equals(name, that.name);
+    }
+
+    @Override
+    public int hashCode() {
+        int result = id.hashCode();
+        result = PRIME * result + (name == null ? 0  : name.hashCode());
+        return result;
+    }
+}

java-collections-maps-3/src/main/java/com/baeldung/map/hashing/MemberWithObjects.java

@@ -0,0 +1,19 @@
+package com.baeldung.map.hashing;
+
+import java.util.Objects;
+
+public class MemberWithObjects extends Member {
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) return true;
+        if (o == null || getClass() != o.getClass()) return false;
+        MemberWithObjects that = (MemberWithObjects) o;
+        return Objects.equals(id, that.id) &&
+                Objects.equals(name, that.name);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(id, name);
+    }
+}