Java Reference
In-Depth Information
// Construct and load the hash. This simulates loading a
// database or reading from a file, or wherever the data is.
Map
<
String
,
String
>
map
=
new
new
HashMap
<
String
,
String
>();
// The hash maps from company name to address.
// In real life this might map to an Address object...
map
.
put
(
"Adobe"
,
"Mountain View, CA"
);
map
.
put
(
"IBM"
,
"White Plains, NY"
);
map
.
put
(
"Learning Tree"
,
"Los Angeles, CA"
);
map
.
put
(
"Microsoft"
,
"Redmond, WA"
);
map
.
put
(
"Netscape"
,
"Mountain View, CA"
);
map
.
put
(
"O'Reilly"
,
"Sebastopol, CA"
);
map
.
put
(
"Sun"
,
"Mountain View, CA"
);
// Two versions of the "retrieval" phase.
// Version 1: get one pair's value given its key
// (presumably the key would really come from user input):
String queryString
=
"O'Reilly"
;
System
.
out
.
println
(
"You asked about "
+
queryString
+
"."
);
String resultString
=
map
.
get
(
queryString
);
System
.
out
.
println
(
"They are located in: "
+
resultString
);
System
.
out
.
println
();
// Version 2: get ALL the keys and values
// (maybe to print a report, or to save to disk)
for
for
(
String key
:
map
.
keySet
()) {
System
.
out
.
println
(
"Key "
+
key
+
"; Value "
+
map
.
get
(
key
));
}
// Version 3: Same but using a Map.Entry lambda
map
.
entrySet
().
forEach
(
mE
->
System
.
out
.
println
(
"Key + "
+
mE
.
getKey
()+
"; Value "
+
mE
.
getValue
()));
}
}
For this version we used both a Java 5
for
loop and a Java 8
forEach()
loop; the latter uses
the return from
entrySet()
, a set of
Map.Entry
, each of which contains one key and one
value (this may be faster on large maps because it avoids going back into the map to get the
value each time through the loop). If you are modifying the list as you are going through it
(e.g., removing elements), either inside the loop or in another thread, then these forms will
