Replace null values with default value in Java Map
Last Updated :
11 Dec, 2018
Given a Map with null values in it, the task is to replace all the null values with a default value.
Examples:
Input: map = {1=1, 2=2, 3=null, 4=4, 5=null, 6=null}, defaultValue = 0
Output: {1=1, 2=2, 3=0, 4=4, 5=0, 6=0}
Input: map = {1=A, 2=B, 3=null, 4=D, 5=null, 6=null}, defaultValue = ‘Z’
Output: {1=A, 2=B, 3=Z, 4=D, 5=Z, 6=Z}
Approach:
- Get the map with null values and the default value to be replaced with.
- Get the set view of the Map using Map.entrySet() method.
- Convert the obtained set view into stream using stream() method.
- Now map the null values to default value with the help of map() method.
- Collect the modified stream into Map using collect() method.
- The null values has been successfully replaced with default value.
Below is the implementation of the above approach:
Example 1: With integers.
import java.util.*;
import java.util.stream.*;
class GFG {
public static <T, K> Map<K, T>
replaceNullValues(Map<K, T> map, T defaultValue)
{
map = map.entrySet()
.stream()
.map(entry -> {
if (entry.getValue() == null )
entry.setValue(defaultValue);
return entry;
})
.collect(Collectors.toMap(Map.Entry::getKey,
Map.Entry::getValue));
return map;
}
public static void main(String[] args)
{
Map<Integer, Integer> map = new HashMap<>();
map.put( 1 , 1 );
map.put( 2 , 2 );
map.put( 3 , null );
map.put( 4 , 4 );
map.put( 5 , null );
map.put( 6 , null );
int defaultValue = 0 ;
System.out.println( "Map with null values: "
+ map);
map = replaceNullValues(map, defaultValue);
System.out.println( "Map with null value replaced: "
+ map);
}
}
|
Output:
Map with null values: {1=1, 2=2, 3=null, 4=4, 5=null, 6=null}
Map with null value replaced: {1=1, 2=2, 3=0, 4=4, 5=0, 6=0}
Example 2: With characters.
import java.util.*;
import java.util.stream.*;
class GFG {
public static <T, K> Map<K, T>
replaceNullValues(Map<K, T> map, T defaultValue)
{
map = map.entrySet()
.stream()
.map(entry -> {
if (entry.getValue() == null )
entry.setValue(defaultValue);
return entry;
})
.collect(Collectors.toMap(Map.Entry::getKey,
Map.Entry::getValue));
return map;
}
public static void main(String[] args)
{
Map<Integer, Character> map = new HashMap<>();
map.put( 1 , 'A' );
map.put( 2 , 'B' );
map.put( 3 , null );
map.put( 4 , 'D' );
map.put( 5 , null );
map.put( 6 , null );
char defaultValue = 'Z' ;
System.out.println( "Map with null values: "
+ map);
map = replaceNullValues(map, defaultValue);
System.out.println( "Map with null value replaced: "
+ map);
}
}
|
Output:
Map with null values: {1=A, 2=B, 3=null, 4=D, 5=null, 6=null}
Map with null value replaced: {1=A, 2=B, 3=Z, 4=D, 5=Z, 6=Z}
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