Find Java field declarations of type String

• Playground Link

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.

Use playground pattern debugger to explore the AST

You can use the playground'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

id: find-field-with-type
language: java
rule:
  kind: field_declaration
  has:
    field: type
    regex: ^String$

Example

@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