# No Threads in Constructors
# Detects thread start() calls in constructors
id: no-threads-in-constructors
name: Threads Should Not Be Started in Constructors
severity: error
category: maintainability
defect_class: correctness
inline_tier: blocking
language: java

message: "Threads should not be started in constructors"

description: |
  Starting threads in constructors can lead to race conditions,
  as the object may not be fully constructed when the thread runs.
  Use a separate start() method or factory pattern instead.

  ✅ FIX: Move thread start to a dedicated method

  ```java
  class Worker {
      private Thread thread;
      
      public Worker() {
          thread = new Thread(this::run);
      }
      
      public void start() {
          thread.start();  // GOOD - explicit start
      }
  }
  ```

query: |
  (constructor_declaration
    body: (constructor_body
      (expression_statement
        (method_invocation
          name: (identifier) @METHOD (#eq? @METHOD "start")) @CALL)))

metavars:
  - METHOD
  - CALL

tags:
  - maintainability
  - java
  - concurrency
  - race-condition
  - cert

examples:
  bad: |
    class Worker {
        public Worker() {
            new Thread(this::run).start();  // BAD - in constructor
        }
    }

  good: |
    class Worker {
        private Thread thread;
        
        public Worker() {
            thread = new Thread(this::run);
        }
        
        public void start() {
            thread.start();  // GOOD - separate method
        }
    }

has_fix: false