HashMap Class in Java

• Map.containsValue(Object value)
  The identity HashMap is used to check that the given object is a value.
  Syntax
  public boolean containsValue(Object value)
  Will return true if the map consists of one or more keys.
  Example
  1. package demo;
  3. import java.util.*;
  5. public class Demo
  6. {
  7. public staticvoid main(String args[])
  8. {
  9. HashMap map =new HashMap();
  10. map.put(99,"Raj");
  11. map.put(199,"Raja");
  12. map.put(299,"Rajan");
  13. System.out.println("CHECK FOR VALUE RAJAN : " +
  14. map.containsValue("Rajan"));
  15. }
  16. }
  Output
  

• Map.get(Object key)
  A value is returned to which the given key is mapped. A null is returned if there is no mapping.
  Syntax
  public A get(Object key)
  Example
  1. package demo;
  3. import java.util.*;
  5. public class Demo
  6. {
  7. public staticvoid main(String args[])
  8. {
  9. HashMap map =new HashMap();
  10. map.put(99,"Raj");
  11. map.put(199,"Raja");
  12. map.put(299,"Rajan");
  13. String val=(String)map.get(99);
  14. System.out.println("VALUE FOR KEY NINETY NINE : " + val);
  15. }
  16. }
  Output
  
• Map.isEmpty( )

  It is checked by this method that the map consists of no key-value mappings.

  Syntax
  public boolean isEmpty()

  It will return true if the given condition is satisfied.

  Example
  1. package demo;
  3. import java.util.*;
  5. public class Demo
  6. {
  7. public staticvoid main(String args[])
  8. {
  9. HashMap map =new HashMap();
  10. map.put(7,"John");
  11. map.put(8,"Johny");
  12. map.put(9,"Jonty");
  13. boolean val=map.isEmpty();
  14. System.out.println("EMPTY: " + val);
  15. }
  16. }
  Output

  
• Map.putAll( )

  It is used to copy mappings from one map to the other.

  Syntax
  public void putAll(Map m)

  Example
  1. package demo;
  3. import java.util.*;
  5. public class Demo
  6. {
  7. public staticvoid main(String args[])
  8. {
  9. HashMap map1 =new HashMap();
  10. HashMap map2 =new HashMap();
  11. map1.put(7,"John");
  12. map1.put(8,"Johny");
  13. map1.put(9,"Jonty");
  14. System.out.println("MAP 1 : "+ map1);
  15. map2.putAll(map1);
  16. System.out.println("\n");
  17. System.out.println("MAP 2 : "+ map2);
  18. }
  19. }
  Output
  
• Map.remove( )

  Mapping is removed for the specific key in the given map.

  Syntax
  public A remove(Object key)

  Example
  1. package demo;
  3. import java.util.*;
  5. public class Demo
  6. {
  7. public staticvoid main(String args[])
  8. {
  9. HashMap map =new HashMap();
  10. map.put(7,"John");
  11. map.put(8,"Johny");
  12. map.put(9,"Jonty");
  13. System.out.println("BEFORE: "+ map);
  14. System.out.println("\n");
  15. map.remove(8);
  16. System.out.println("AFTER: "+ map);
  17. }
  18. }
  Output
  
• Map.values( )

  It will return all the values of the map.

  Syntax
  public Collection values()

  Example
  1. package demo;
  3. import java.util.*;
  5. public class Demo
  6. {
  7. public staticvoid main(String args[])
  8. {
  9. HashMap map =new HashMap();
  10. map.put(7,"John");
  11. map.put(8,"Johny");
  12. map.put(9,"Jonty");
  13. System.out.println("VALUES: "+ map.values());
  14. }
  15. }
  Output
  

Constructors Supported by HasMap

• HashMap( )
  A default HashMap is created by this constructor.
  
• HashMap(m)
  HashMap is initialized by this constructor.
  
• HashMap( int capacity)
  Capacity is initialized by this constructor.
  
• HashMap(int capacity, float fillRatio)
  Capacity and the fill ratio are initialized by this constructor.

Summary