HashMap方法/参数

Question

See the following class definition using a HashMap.

Why is it not necessary to pass formal parameters of the methods to local parameters as I did in the second method?

import java.util.HashMap;

public class MapTester
{
    private HashMap<String, String> phoneBook = new HashMap<String, String> ();

    public MapTester()
    {
        phoneBook.put("Homer Jay Simpson", "(531) 9392 4587");
        phoneBook.put("Charles Montgomery Burns", "(531) 5432 1945");
        phoneBook.put("Apu Nahasapeemapetilon", "(531) 4234 4418");        
    }    

    public void enterNumber(String name, String number)
    {       
        phoneBook.put(name, number);
    }

    public String lookupNumber(String _name) 
    {          
      name = _name;  
      return phoneBook.get(name);
    }   
}

Answer 1

It is not necessary to copy the parameter to a local variable, because then you would have two copies of the same variable ( name and _name ) while you need only one.

Moreover, you would probably need to change the line to

String name = _name;

to make it compile.

Answer 2

You can directly use formal parameters without copying it into local parameter because it will get original value, when function is called.

 public String lookupNumber(String _name) 
 {          
      return phoneBook.get(_name);
 }  

It is necessary only in the case of getter and setter, where you set the local variable using setter and get updated value using getter.