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PMD is a tool that looks for potential problems like possible bugs, dead code, suboptimal code, overcomplicated expressions or duplicate code.

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Partially created objects can be returned by the Double Checked Locking pattern when used in Java. An optimizing JRE may assign a reference to the baz variable before it creates the object the reference is intended to point to. More details. Example :
public class Foo {
  Object baz;
  Object bar() {
    if(baz == null) { //baz may be non-null yet not fully created
      synchronized(this){
        if(baz == null){
          baz = new Object();
        }
      }
    }
    return baz;
  }
}