Transfer backend into backend branch

also build their secondary constructor

.idea/inspectionProfiles/Project_Default.xml

+<component name="InspectionProjectProfileManager">
+  <profile version="1.0">
+    <option name="myName" value="Project Default" />
+    <inspection_tool class="DuplicatedCode" enabled="true" level="WEAK WARNING" enabled_by_default="true">
+      <Languages>
+        <language minSize="47" name="Java" />
+      </Languages>
+    </inspection_tool>
+  </profile>
+</component>
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