put common luasnip functions in a seperate file and modify some

java snippets

lua/core/snippets/functions.lua

@@ -0,0 +1,3 @@
+function file_name(args, parent, user_args)
+  return vim.fn.expand("%:t:r")
+end

lua/snippets/java.lua

@@ -1,8 +1,5 @@
 require('core.snippets.shorthands')
-
+require('core.snippets.functions')
-local function file_name(args, parent, user_args)
-  return vim.fn.expand("%:t:r")
-end
 
 return {
   -- method snippet
@@ -34,6 +31,12 @@ return {
     t({ "", "}" }),
   }),
 
+  s("main", {
+    t({ "public static void main(String[] args) {", "\t" }),
+    i(0),
+    t({ "", "}" }),
+  }),
+
   -- constructor snippet
   s("constr", {
     c(1, {
@@ -59,14 +62,18 @@ return {
     c(1, {
       t("public "),
       t("private "),
-      t("protected ")
+      t("protected "),
+      t("")
     }),
     c(2, {
       t("class "),
       t("interface ")
     }),
-    f(file_name, {}),
     c(3, {
+      i(0, "MyClass"),
+      f(file_name, {})
+    }),
+    c(4, {
       t(" "),
       sn(nil, { t({" implements "}), i(1), t(" ") }),
       sn(nil, { t({" extends "}), i(1), t(" ") }),