yes there's a bit of java in my nvim config why do you ask?

lua/conf/plugins/treesj.lua

@@ -0,0 +1,14 @@
+local misc = require('core.misc')
+local map = misc.map
+
+return { 'Wansmer/treesj',
+  disable = vim.version().minor < 9,
+  requires = 'nvim-treesitter/nvim-treesitter',
+  function()
+    require('treesj').setup {
+      use_default_keymaps = false,
+    }
+
+    map('n', '<leader>j', require('treesj').toggle, { desc = 'fold code' })
+  end
+}