2011-1-6 Java traverses all elements of Map
// Map = getmap (); For (Object OBJ: map. keyset () {object key = OBJ; object value = map. get (OBJ);} // map = getmap (); iterator iter = map before jdk1.5. entryset (). iterator (); While (ITER. hasnext () {map. entry entry = (map. entry) ITER. next (); object key = entry. getkey (); object value = entry. getvalue ();}
Traversing K-V
/* First: entryset only traverses once: it puts the key and value into entry */map = getmap (); iterator iter = map. entryset (). iterator (); While (ITER. hasnext () {map. entry entry = (map. entry) ITER. next (); object key = entry. getkey (); object val = entry. getvalue ();} // efficient. Use this method/* Second: The keyset actually traverses twice: once converted to iterator; the value corresponding to the key is retrieved again. */Map = getmap (); iterator iter = map. keyset (). iterator (); While (ITER. hasnext () {object key = ITER. next (); object val = map. get (key);} // Low Efficiency