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DoubleCheckedLocking


DoubleCheckedLocking
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.  For more details see http://www.javaworld.com/javaworld/jw-02-2001/jw-0209-double.html.
      
		
		
		    
		    
    		    
    		    
    		    

    		    This rule is defined by the following Java class:
    		    net.sourceforge.pmd.rules.DoubleCheckedLocking
    		    
		    
	    
	    
        
        
        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;
  }
}