[API] Remove lazy-created sructs and add methods to verify struct pointer

imgui-binding/src/main/java/imgui/binding/ImGuiStruct.java

@@ -3,11 +3,13 @@ package imgui.binding;
 import imgui.ImGui;
 
 /**
- * Class provides a communication layer between binding and Dear ImGui library though the "pointer" field.
+ * Class provides a communication layer between binding and Dear ImGui library through the "pointer" field.
  */
 public abstract class ImGuiStruct {
     /**
-     * Pointer to the natively allocated object,
+     * Pointer to the natively allocated object.
+     * Could be zero if JNI returned NULL instead of the real object.
+     * For such cases methods {@link #isValidPtr()} and {@link #isNotValidPtr()} could be used to verify that object points to the real object.
      */
     public long ptr;
 
@@ -15,4 +17,22 @@ public abstract class ImGuiStruct {
         ImGui.init();
         this.ptr = ptr;
     }
+
+    /**
+     * Shows if object pointer is valid and does it point to the existing object.
+     *
+     * @return true, if pointer is valid
+     */
+    public final boolean isValidPtr() {
+        return ptr != 0;
+    }
+
+    /**
+     * Shows if object pointer is valid and does it point to the existing object.
+     *
+     * @return true, if pointer is invalid
+     */
+    public final boolean isNotValidPtr() {
+        return !isValidPtr();
+    }
 }