Getting custom key from map based on comparator etc.

[Anubhav Anand]

I have the code scenario as below. The map contains both Key and Value as beans. I want to get value from map, even when all fields of the key may not be present i.e. are null. Is there a way to do this?

import java.util.HashMap;
import java.util.Map;

import org.apache.commons.lang.builder.EqualsBuilder;
import org.apache.commons.lang.builder.HashCodeBuilder;

public class KeyDemo
{
	private static Map<Key, Value> map;
	static
	{
		map = new HashMap<Key, Value>();
		Key k1 = new Key();
		k1.setAge("20");
		k1.setName("Randy");
		Value v1 = new Value();
		v1.setMobile("123");
		v1.setOffice("456");

		Key k2 = new Key();
		k2.setAge("30");
		k2.setName("Mandy");
		Value v2 = new Value();
		v2.setMobile("789");
		v2.setOffice("901");

		map.put(k1, v1);
		map.put(k2, v2);
	}

	public static void main(String[] args)
	{
		Key k1 = new Key();
		k1.setAge("20");
		k1.setName("Randy");

		Key k2 = new Key();
		k2.setAge("30");
		k2.setName("Mandy");

		Key k3 = new Key();
		k3.setAge("30");
		k3.setName(null);

		System.out.println(map.get(k1).getMobile());
		System.out.println(map.get(k2).getMobile());

		System.out.println(map.get(k3).getMobile());
	}
}

class Key
{
	private String name;
	private String age;

	public String getName()
	{
		return name;
	}

	public void setName(String name)
	{
		this.name = name;
	}

	public String getAge()
	{
		return age;
	}

	public void setAge(String age)
	{
		this.age = age;
	}

	@Override
	public boolean equals(Object obj)
	{
		Key k = (Key) obj;
		return new EqualsBuilder().append(age, k.age).append(name, k.name).isEquals();
	}

	@Override
	public int hashCode()
	{
		return new HashCodeBuilder(17, 31).append(age).append(name).toHashCode();
	}
}

class Value
{
	private String mobile;
	private String office;

	public String getMobile()
	{
		return mobile;
	}

	public void setMobile(String mobile)
	{
		this.mobile = mobile;
	}

	public String getOffice()
	{
		return office;
	}

	public void setOffice(String office)
	{
		this.office = office;
	}

	@Override
	public boolean equals(Object obj)
	{
		Value v = (Value) obj;
		return new EqualsBuilder().append(mobile, v.mobile).append(office, v.office).isEquals();
	}

	@Override
	public int hashCode()
	{
		return new HashCodeBuilder(17, 31).append(mobile).append(office).toHashCode();
	}
}

So precisely, i want the K3 to work as well somehow. Not sure if I am thinking straight , but need this or something on this line to work
Thanks in advance.

- Anubhav

[Seetharaman Venkatasamy]

Anubhav Anand wrote:i want the K3 to work as well somehow.

what value you are expecting? what are the attribute should be unique in the Key object?

[Anubhav Anand]

Lets say for this example, age will always be unique. But I don't want to maintain the same set of vales for age and name keys into multiple maps.
So, in this case I want K3 to return the value same as K2.

Thanks,
Anubhav

[Seetharaman Venkatasamy]

then change your equals and hashCode implementation to

  @Override  
     public boolean equals(Object obj)  
     {  
         Key k = (Key) obj;  
         return new EqualsBuilder().append(age, k.age).isEquals();  
     }  
   
     @Override  
     public int hashCode()  
     {  
         return new HashCodeBuilder(17, 31).append(age).toHashCode();  
     }  

i.e, exclude the name attribute from your equals and hasCode implementation

[Anubhav Anand]

Thanks Seetharaman.
Is there a way to also achieve if-else. Precisely what if say the name was unique as well independently. Because the actual key bean has a lot of attributes say 10, and the combination of all 10 would be unique, but at times even 6 may be able to provide the required unique constraint.
So, i want to achieve something like the nvl function in SQL.

So, in this case make it work for say name, or age, or both.

Thanks,
Anubhav

[Seetharaman Venkatasamy]

sort of, implement your equals and hashCode as your needs.

[Campbell Ritchie]

Seetharaman Venkatasamy wrote:then change your equals and hashCode implementation to

  @Override  
     public boolean equals(Object obj)  
     {  
         Key k = (Key) obj;  
         return new EqualsBuilder().append(age, k.age).isEquals();  
     }  
   
/**
 * This method will only work if you have the appropriate
 * HashCodeBuilder class available
 */
     @Override  
     public int hashCode()  
     {  
         return new HashCodeBuilder(17, 31).append(age).toHashCode();  
     }  

. . .

That equals method won't work; it will be prone to Exceptions because of the cast. You need to test for the type of the obj parameter before using it. I would suggest you write it like this.

@Override
public boolean equals(Object obj)
{
   return obj == this ||
   obj != null &&
   obj.getClass() == this.getClass() &&
   ((Key)obj).age.equals(this.age) &&
   ((Key)obj).name.equals(this.name);
}

This will still suffer problems if you allow null values for age and name. Then you would be better off like this:
... ((Key)obj).age == null ? this.age == null : ((Key)obj).age.equals(this.age) && ...
Obviously you can use as many fields or as few as you wish in the equals method, but yo umust use the same fields in the hashCode method.