treewide: flatten single file modules

Some files don't need nesting and can be root level again to reduce
conflicts with other PRs.

Signed-off-by: Austin Horstman <khaneliman12@gmail.com>

modules/programs/java.nix

@@ -0,0 +1,40 @@
+# This module provides JAVA_HOME, with a different way to install java locally.
+# This module is modified from the NixOS module `programs.java`
+{
+  config,
+  lib,
+  pkgs,
+  ...
+}:
+let
+
+  cfg = config.programs.java;
+
+in
+{
+  meta.maintainers = with lib.maintainers; [ ShamrockLee ];
+
+  options = {
+    programs.java = {
+      enable = lib.mkEnableOption "" // {
+        description = ''
+          Install the Java development kit and set the
+          {env}`JAVA_HOME` variable.
+        '';
+      };
+
+      package = lib.mkPackageOption pkgs "java" {
+        default = "jdk";
+        example = "pkgs.jre";
+      };
+    };
+  };
+
+  config = lib.mkIf cfg.enable {
+    home.packages = [ cfg.package ];
+
+    # some instances of `jdk-linux-base.nix` pass through `result` without turning it onto a path-string.
+    # while I suspect this is incorrect, the documentation is unclear.
+    home.sessionVariables.JAVA_HOME = "${cfg.package.home}";
+  };
+}