fix: add new example

Author: HerringtonDarkholme

website/catalog/java/find-field-with-type.md

@@ -0,0 +1,65 @@
+## Find Java field declarations of type String
+
+* [Playground Link](/playground.html#eyJtb2RlIjoiQ29uZmlnIiwibGFuZyI6ImphdmEiLCJxdWVyeSI6ImAkVEFHYCIsInJld3JpdGUiOiIiLCJzdHJpY3RuZXNzIjoic21hcnQiLCJzZWxlY3RvciI6IiIsImNvbmZpZyI6InJ1bGU6XG4gIGtpbmQ6IGZpZWxkX2RlY2xhcmF0aW9uXG4gIGhhczpcbiAgICBmaWVsZDogdHlwZVxuICAgIHJlZ2V4OiBeU3RyaW5nJCIsInNvdXJjZSI6IkBDb21wb25lbnRcbmNsYXNzIEFCQyBleHRlbmRzIE9iamVjdHtcbiAgICBAUmVzb3VyY2VcbiAgICBwcml2YXRlIGZpbmFsIFN0cmluZyB3aXRoX2Fubm87XG5cbiAgICBwcml2YXRlIGZpbmFsIFN0cmluZyB3aXRoX211bHRpX21vZDtcblxuICAgIHB1YmxpYyBTdHJpbmcgc2ltcGxlO1xufSJ9)
+
+### Description
+
+To extract all Java field names of type `String` is not as straightforward as one might think. A simple pattern like `String $F;` would only match fields declared without any modifiers or annotations. However, a pattern like `$MOD String $F;` cannot be correctly parsed by tree-sitter.
+
+:::details Use playground pattern debugger to explore the AST
+
+You can use the [playground](https://ast-grep.github.io/playground.html#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)'s pattern tab to visualize the AST of `class A { $MOD String $F; }`.
+
+```
+field_declaration
+  $MOD
+  variable_declarator
+    identifier: String
+  ERROR
+    identifier: $F
+```
+
+Tree-sitter does not think `$MOD` is a valid modifier, so it produces an `ERROR`.
+
+While the valid AST for code like `private String field;` produces different AST structures:
+
+```
+field_declaration
+  modifiers
+  type_identifier
+  variable_declarator
+    identifier: field
+```
+
+:::
+
+A more robust approach is to use a structural rule that targets `field_declaration` nodes and applies a `has` constraint on the `type` child node to match the type `String`. This method effectively captures fields regardless of their modifiers or annotations.
+
+### YAML
+
+```yaml
+id: find-field-with-type
+language: java
+rule:
+  kind: field_declaration
+  has:
+    field: type
+    regex: ^String$
+```
+
+### Example
+
+```java {3-4,6,8}
+@Component
+class ABC extends Object{
+    @Resource
+    private final String with_anno;
+
+    private final String with_multi_mod;
+
+    public String simple;
+}
+```
+
+### Contributed by
+Inspired by the post [discussion](https://github.com/ast-grep/ast-grep/discussions/2195)

website/catalog/java/index.md

@@ -2,4 +2,5 @@
 
 This page curates a list of example ast-grep rules to check and to rewrite Java code.
 
-<!--@include: ./no-unused-vars.md-->
+<!--@include: ./no-unused-vars.md-->
+<!--@include: ./find-field-with-type.md-->

website/catalog/java/no-unused-vars.md

@@ -1,4 +1,4 @@
-## No Unused Vars in Java
+## No Unused Vars in Java <Badge type="tip" text="Has Fix" />
 
 * [Playground Link](/playground.html#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)