I now have a.txt and b.txt files, and the diff I got by comparing these two files through Java
diff:
--- test1.txt
+++ test2.txt
@@ -10,0 +10,2 @@
+insert1;
+insert2;
@@ -19,2 +21,3 @@
-window.upList = [];
-window.downList = [];
+break;
My example is as follows:

结果如下:

How can I combine diff with a.txt and b.txt to get a complete content comparison?