BAEL-2969: Copying Sets in Java

core-java-modules/core-java-collections-set/src/main/java/com/baeldung/set/CopySets.java

@@ -0,0 +1,74 @@
+package com.baeldung.set;
+
+import java.io.Serializable;
+import java.util.HashSet;
+import java.util.Objects;
+import java.util.Set;
+import java.util.stream.Collectors;
+
+import org.apache.commons.lang.SerializationUtils;
+
+import com.google.gson.Gson;
+
+public class CopySets {
+
+    public static <T> Set<T> copyByConstructor(Set<T> original) {
+        Set<T> copy = new HashSet<>(original);
+        return copy;
+    }
+
+    public static <T> Set<T> copyBySetAddAll(Set<T> original) {
+        Set<T> copy = new HashSet<>();
+        copy.addAll(original);
+        return copy;
+    }
+
+    public static <T> Set<T> copyBySetClone(HashSet<T> original) {
+        Set<T> copy = (Set<T>) original.clone();
+        return copy;
+    }
+
+    public static <T> Set<T> copyByJson(Set<T> original) {
+        Gson gson = new Gson();
+        String jsonStr = gson.toJson(original);
+        Set<T> copy = gson.fromJson(jsonStr, Set.class);
+
+        return copy;
+    }
+
+    public static <T extends Serializable> Set<T> copyByApacheCommonsLang(Set<T> original) {
+        Set<T> copy = new HashSet<>();
+        for (T item : original) {
+            copy.add((T) SerializationUtils.clone(item));
+        }
+        return copy;
+    }
+
+    public static <T> void copyByStreamsAPI(Set<T> original) {
+        Set<T> copy1 = original.stream()
+            .collect(Collectors.toSet());
+
+        // Skip the first element
+        Set<T> copy2 = original.stream()
+            .skip(1)
+            .collect(Collectors.toSet());
+
+        // Filter by comparing the types and attributes
+        Set<T> copy3 = original.stream()
+            .filter(f -> f.getClass()
+                .equals(Integer.class))
+            .collect(Collectors.toSet());
+
+        // Null check in case of expecting null values
+        Set<T> copy4 = original.stream()
+            .filter(Objects::nonNull)
+            .collect(Collectors.toSet());
+
+    }
+
+    public static <T> Set<T> copyByJava8(Set<T> original) {
+        Set<T> copy = Set.copyOf(original);
+        return copy;
+    }
+
+}