How do I find the value of an unknown key in my HashMap and convert it into an int?
Doesnt really need much of an explanation, just wondering what would be the best and efficient way to do that. The HashMap has only one Key left, (checked with map.size() == 1), however the Key is unknown. The HashMap is <Integer, Integer>.
Thanks a lot to everyone trying to help!
java
edited Nov 23 '18 at 20:08
JB Nizet
535k52862995
asked Nov 23 '18 at 20:06
FABULATORFABULATOR
33
add a comment |
Doesnt really need much of an explanation, just wondering what would be the best and efficient way to do that. The HashMap has only one Key left, (checked with map.size() == 1), however the Key is unknown. The HashMap is <Integer, Integer>.
Thanks a lot to everyone trying to help!
java
edited Nov 23 '18 at 20:08
JB Nizet
535k52862995
asked Nov 23 '18 at 20:06
FABULATORFABULATOR
33
1
You can use Map#keySet() to obtain a set of keys. The rest should be self explanatory. You could also use Map#entrySet(), and iterate over these entries. An entry is an object that contains a key and a value. For example,for (Entry<Integer, Integer> entry : map.entrySet()) { print(entry.getKey() + entry.getValue(); }
– PhaseRush
Nov 23 '18 at 20:09
add a comment |
Doesnt really need much of an explanation, just wondering what would be the best and efficient way to do that. The HashMap has only one Key left, (checked with map.size() == 1), however the Key is unknown. The HashMap is <Integer, Integer>.
Thanks a lot to everyone trying to help!
java
edited Nov 23 '18 at 20:08
JB Nizet
535k52862995
asked Nov 23 '18 at 20:06
FABULATORFABULATOR
33
Doesnt really need much of an explanation, just wondering what would be the best and efficient way to do that. The HashMap has only one Key left, (checked with map.size() == 1), however the Key is unknown. The HashMap is <Integer, Integer>.
Thanks a lot to everyone trying to help!
java
java
edited Nov 23 '18 at 20:08
JB Nizet
535k52862995
asked Nov 23 '18 at 20:06
FABULATORFABULATOR
33
edited Nov 23 '18 at 20:08
JB Nizet
535k52862995
asked Nov 23 '18 at 20:06
FABULATORFABULATOR
33
edited Nov 23 '18 at 20:08
JB Nizet
535k52862995
edited Nov 23 '18 at 20:08
JB Nizet
535k52862995
edited Nov 23 '18 at 20:08
JB Nizet
535k52862995
535k52862995
asked Nov 23 '18 at 20:06
FABULATORFABULATOR
33
asked Nov 23 '18 at 20:06
FABULATORFABULATOR
33
asked Nov 23 '18 at 20:06
FABULATORFABULATOR
33
33
1
You can use Map#keySet() to obtain a set of keys. The rest should be self explanatory. You could also use Map#entrySet(), and iterate over these entries. An entry is an object that contains a key and a value. For example,for (Entry<Integer, Integer> entry : map.entrySet()) { print(entry.getKey() + entry.getValue(); }
– PhaseRush
Nov 23 '18 at 20:09
add a comment |
1
You can use Map#keySet() to obtain a set of keys. The rest should be self explanatory. You could also use Map#entrySet(), and iterate over these entries. An entry is an object that contains a key and a value. For example,for (Entry<Integer, Integer> entry : map.entrySet()) { print(entry.getKey() + entry.getValue(); }
– PhaseRush
Nov 23 '18 at 20:09
1
1
You can use Map#keySet() to obtain a set of keys. The rest should be self explanatory. You could also use Map#entrySet(), and iterate over these entries. An entry is an object that contains a key and a value. For example,
for (Entry<Integer, Integer> entry : map.entrySet()) { print(entry.getKey() + entry.getValue(); }– PhaseRush
Nov 23 '18 at 20:09
You can use Map#keySet() to obtain a set of keys. The rest should be self explanatory. You could also use Map#entrySet(), and iterate over these entries. An entry is an object that contains a key and a value. For example,
for (Entry<Integer, Integer> entry : map.entrySet()) { print(entry.getKey() + entry.getValue(); }– PhaseRush
Nov 23 '18 at 20:09
add a comment |
2 Answers
2
active
oldest
votes
As .keySet() and .entrySet() returns Set you can't direct use a get operation like with List
Through
Streamyou can :
int unknowKey = map.keySet().stream()
.findAny()
.orElseThrow(IllegalArgumentException::new);
Or, with
Iterator:
int unknowKey = map.keySet().iterator().next();
In term of efficiency, iterator is really superior:
Benchmark Mode Cnt Score Error Units
MyBench.iterator avgt 5 10,663 ± 0,175 ns/op
MyBench.stream avgt 5 47,960 ± 4,819 ns/op
answered Nov 23 '18 at 20:13
azroazro
10.5k41438
Nice analysis :) ... I think conversion to a stream takes time maybe
– mettleap
Nov 23 '18 at 20:39
add a comment |
Use the keySet method to get the key in a set and then iterate through the set to get the key, like so,
HashMap<Integer, Integer> map = new HashMap<Integer, Integer>();
map.put(5, 1); // some map with only one key-value pair
int a = map.keySet().iterator().next(); // obtain keyset, get iterator and get the next element (since you know map size is 1)
System.out.println(a);
answered Nov 23 '18 at 20:11
mettleapmettleap
1,080216
add a comment |
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
As .keySet() and .entrySet() returns Set you can't direct use a get operation like with List
Through
Streamyou can :
int unknowKey = map.keySet().stream()
.findAny()
.orElseThrow(IllegalArgumentException::new);
Or, with
Iterator:
int unknowKey = map.keySet().iterator().next();
In term of efficiency, iterator is really superior:
Benchmark Mode Cnt Score Error Units
MyBench.iterator avgt 5 10,663 ± 0,175 ns/op
MyBench.stream avgt 5 47,960 ± 4,819 ns/op
answered Nov 23 '18 at 20:13
azroazro
10.5k41438
Nice analysis :) ... I think conversion to a stream takes time maybe
– mettleap
Nov 23 '18 at 20:39
add a comment |
As .keySet() and .entrySet() returns Set you can't direct use a get operation like with List
Through
Streamyou can :
int unknowKey = map.keySet().stream()
.findAny()
.orElseThrow(IllegalArgumentException::new);
Or, with
Iterator:
int unknowKey = map.keySet().iterator().next();
In term of efficiency, iterator is really superior:
Benchmark Mode Cnt Score Error Units
MyBench.iterator avgt 5 10,663 ± 0,175 ns/op
MyBench.stream avgt 5 47,960 ± 4,819 ns/op
answered Nov 23 '18 at 20:13
azroazro
10.5k41438
Nice analysis :) ... I think conversion to a stream takes time maybe
– mettleap
Nov 23 '18 at 20:39
add a comment |
As .keySet() and .entrySet() returns Set you can't direct use a get operation like with List
Through
Streamyou can :
int unknowKey = map.keySet().stream()
.findAny()
.orElseThrow(IllegalArgumentException::new);
Or, with
Iterator:
int unknowKey = map.keySet().iterator().next();
In term of efficiency, iterator is really superior:
Benchmark Mode Cnt Score Error Units
MyBench.iterator avgt 5 10,663 ± 0,175 ns/op
MyBench.stream avgt 5 47,960 ± 4,819 ns/op
answered Nov 23 '18 at 20:13
azroazro
10.5k41438
As .keySet() and .entrySet() returns Set you can't direct use a get operation like with List
Through
Streamyou can :
int unknowKey = map.keySet().stream()
.findAny()
.orElseThrow(IllegalArgumentException::new);
Or, with
Iterator:
int unknowKey = map.keySet().iterator().next();
In term of efficiency, iterator is really superior:
Benchmark Mode Cnt Score Error Units
MyBench.iterator avgt 5 10,663 ± 0,175 ns/op
MyBench.stream avgt 5 47,960 ± 4,819 ns/op
answered Nov 23 '18 at 20:13
azroazro
10.5k41438
edited Nov 23 '18 at 20:21
answered Nov 23 '18 at 20:13
azroazro
10.5k41438
answered Nov 23 '18 at 20:13
azroazro
10.5k41438
answered Nov 23 '18 at 20:13
azroazro
10.5k41438
10.5k41438
Nice analysis :) ... I think conversion to a stream takes time maybe
– mettleap
Nov 23 '18 at 20:39
add a comment |
Nice analysis :) ... I think conversion to a stream takes time maybe
– mettleap
Nov 23 '18 at 20:39
Nice analysis :) ... I think conversion to a stream takes time maybe
– mettleap
Nov 23 '18 at 20:39
Nice analysis :) ... I think conversion to a stream takes time maybe
– mettleap
Nov 23 '18 at 20:39
add a comment |
Use the keySet method to get the key in a set and then iterate through the set to get the key, like so,
HashMap<Integer, Integer> map = new HashMap<Integer, Integer>();
map.put(5, 1); // some map with only one key-value pair
int a = map.keySet().iterator().next(); // obtain keyset, get iterator and get the next element (since you know map size is 1)
System.out.println(a);
answered Nov 23 '18 at 20:11
mettleapmettleap
1,080216
add a comment |
Use the keySet method to get the key in a set and then iterate through the set to get the key, like so,
HashMap<Integer, Integer> map = new HashMap<Integer, Integer>();
map.put(5, 1); // some map with only one key-value pair
int a = map.keySet().iterator().next(); // obtain keyset, get iterator and get the next element (since you know map size is 1)
System.out.println(a);
answered Nov 23 '18 at 20:11
mettleapmettleap
1,080216
add a comment |
Use the keySet method to get the key in a set and then iterate through the set to get the key, like so,
HashMap<Integer, Integer> map = new HashMap<Integer, Integer>();
map.put(5, 1); // some map with only one key-value pair
int a = map.keySet().iterator().next(); // obtain keyset, get iterator and get the next element (since you know map size is 1)
System.out.println(a);
answered Nov 23 '18 at 20:11
mettleapmettleap
1,080216
Use the keySet method to get the key in a set and then iterate through the set to get the key, like so,
HashMap<Integer, Integer> map = new HashMap<Integer, Integer>();
map.put(5, 1); // some map with only one key-value pair
int a = map.keySet().iterator().next(); // obtain keyset, get iterator and get the next element (since you know map size is 1)
System.out.println(a);
answered Nov 23 '18 at 20:11
mettleapmettleap
1,080216
answered Nov 23 '18 at 20:11
mettleapmettleap
1,080216
answered Nov 23 '18 at 20:11
mettleapmettleap
1,080216
answered Nov 23 '18 at 20:11
mettleapmettleap
1,080216
1,080216
add a comment |
add a comment |
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1
You can use Map#keySet() to obtain a set of keys. The rest should be self explanatory. You could also use Map#entrySet(), and iterate over these entries. An entry is an object that contains a key and a value. For example,
for (Entry<Integer, Integer> entry : map.entrySet()) { print(entry.getKey() + entry.getValue(); }– PhaseRush
Nov 23 '18 at 20:09