EN
Java - iterate over keys in HashMap
8 points
Short solution - using forEach() from Java 8:
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Map<String, Integer> map = new HashMap<>();2
3
map.keySet().forEach(key -> {4
// use key variable5
System.out.println("Key: " + key);6
});Short solution - using for loop and Map keySet():
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Map<String, Integer> map = new HashMap<>();2
3
for (String key : map.keySet()) {4
System.out.println("Key: " + key);5
}Short solution - iterate over entire map and use only keys with forEach() from Java 8:
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Map<String, Integer> map = new HashMap<>();2
3
map.forEach((key, value) -> {4
// we use only key variable5
System.out.println("Key: " + key);6
});Short solution - iterate over entire map with entrySet() and use only keys:
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Map<String, Integer> map = new HashMap<>();2
3
for (Map.Entry<String, Integer> entry : map.entrySet()) {4
String key = entry.getKey();5
// Integer value = entry.getValue();6
7
System.out.println("Key: " + key);8
}xxxxxxxxxx1
import java.util.HashMap;2
import java.util.Map;3
4
public class Example1 {5
6
public static void main(String[] args) {7
8
Map<String, Integer> map = new HashMap<>();9
map.put("A", 10);10
map.put("B", 20);11
map.put("C", 30);12
13
map.keySet().forEach(key -> {14
// use key variable15
System.out.println("Key: " + key);16
});17
}18
}Output:
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Key: A2
Key: B3
Key: Cxxxxxxxxxx1
import java.util.HashMap;2
import java.util.Map;3
4
public class Example2 {5
6
public static void main(String[] args) {7
8
Map<String, Integer> map = new HashMap<>();9
map.put("A", 10);10
map.put("B", 20);11
map.put("C", 30);12
13
for (String key : map.keySet()) {14
System.out.println("Key: " + key);15
}16
}17
}Output:
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Key: A2
Key: B3
Key: CWe can also iterate over entire map and use only keys with forEach() from Java 8
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import java.util.HashMap;2
import java.util.Map;3
4
public class Example3 {5
6
public static void main(String[] args) {7
8
Map<String, Integer> map = new HashMap<>();9
map.put("A", 10);10
map.put("B", 20);11
map.put("C", 30);12
13
map.forEach((key, value) -> {14
// we use only key variable15
System.out.println("Key: " + key);16
});17
}18
}Output:
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Key : A2
Key : B3
Key : CWe can also iterate over entire map with entrySet() and use only keys
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import java.util.HashMap;2
import java.util.Map;3
4
public class Example4 {5
6
public static void main(String[] args) {7
8
Map<String, Integer> map = new HashMap<>();9
map.put("A", 10);10
map.put("B", 20);11
map.put("C", 30);12
13
for (Map.Entry<String, Integer> entry : map.entrySet()) {14
String key = entry.getKey();15
// Integer value = entry.getValue();16
17
System.out.println("Key: " + key);18
}19
}20
}Output:
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Key : A2
Key : B3
Key : C