Added Materials Description class

Author: Anirav Kareddy

src/main/java/software/amazon/encryption/s3/materials/MaterialsDescription.java

@@ -0,0 +1,44 @@
+// Copyright Amazon.com Inc. or its affiliates. All Rights Reserved.
+// SPDX-License-Identifier: Apache-2.0
+
+package software.amazon.encryption.s3.materials;
+
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.Map;
+
+public class MaterialsDescription {
+    private final Map<String, String> materialsDescription;
+
+    private MaterialsDescription(Builder builder) {
+        this.materialsDescription = Collections.unmodifiableMap(new HashMap<>(builder.materialsDescription));
+    }
+    public static Builder builder() {
+        return new Builder();
+    }
+    public Map<String, String> getDescription() {
+      return this.materialsDescription;
+    }
+    public static class Builder {
+        private final Map<String, String> materialsDescription = new HashMap<>();
+        public Builder put(String key, String value) {
+            if (key == null || value == null) {
+                throw new IllegalArgumentException("Key and value must not be null");
+            }
+            materialsDescription.put(key, value);
+            return this;
+        }
+        public Builder putAll(Map<String, String> description) {
+          if (description == null) {
+            throw new IllegalArgumentException("Description must not be null");
+          }
+          for (Map.Entry<String, String> entry : description.entrySet()) {
+            put(entry.getKey(), entry.getValue());
+          }
+          return this;
+        }
+        public MaterialsDescription build() {
+          return new MaterialsDescription(this);
+        }
+    }
+}