Phone Directory using TreeMap
Objective
In this lab, we will create a basic PhoneDirectory by using a TreeMap to store directory entries.
Learning Objective
By the end of this lesson, learners will be able to utilize the TreeMap.
Scenario
Finds the phone number, if any, for a given name and returns the phone number associated with the name if the name does not occur in the phone directory, and then returns the value as null.
Associates a given name with a given phone number. If the name already exists in the phone directory, the new number replaces the old one. Otherwise, a new name/number pair is added. The name and number should both be non-null. An IllegalArgumentException is thrown if this is not the case.
Instructions
Step 1
Create a new Java project and create a new Class named “PhoneDirectoryWithTreeMap,” and then write the below code in the class.
import java.util.TreeMap;
import java.util.Map;
public class PhoneDirectoryWithTreeMap {
/**
* The TreeMap that will store the data. Both key and value are
* of type String. The key represents a name and the value represents
* the associated phone number.
*/
private TreeMap<String,String> data;
/**
* Constructor creates an initially empty directory.
*/
public PhoneDirectoryWithTreeMap() {
this.data = new TreeMap<String,String>();
}
/**
* Finds the phone number, if any, for a given name.
* @return The phone number associated with the name; if the name does
* not occur in the phone directory, then the return value is null.
*/
public String getNumber( String name ) {
return this.data.get(name);
}
/**
* Associates a given name with a given phone number. If the name
* already exists in the phone directory, then the new number replaces
* the old one. Otherwise, a new name/number pair is added. The
* name and number should both be non-null. An IllegalArgumentException
* is thrown if this is not the case. */
public void putNumber( String name, String number ) {
if (name == null || number == null)
throw new IllegalArgumentException("name and number cannot be null");
this.data.put(name,number);
}
/** Write the contents of the phone directory to System.out.
*/
public void print() {
for ( Map.Entry<String,String> entry : this.data.entrySet() )
System.out.println( entry.getKey() + ": " + entry.getValue() );
}
} // end class PhoneDirectoryWithTreeMap
Step 2
Create a new Java project and create a new Class named “TestPhoneDirectoryWithTreeMap,” and then write the code below in the class.
public class TestPhoneDirectoryWithTreeMap {
public static void main(String[] args) {
PhoneDirectoryWithTreeMap directory = new PhoneDirectoryWithTreeMap();
System.out.println("This program creates a PhoneDirectoryWithTreeMap and");
System.out.println("adds several entries. It then prints the contents of");
System.out.println("directory and does a few lookups.");
System.out.println();
directory.putNumber("Fred","555-1234");
directory.putNumber("Barney","555-2345");
directory.putNumber("Wilma","555-3456");
directory.putNumber("Wilma","555-3456");
directory.putNumber("Wilma","555-2563");
// directory.putNumber("James",null);
//directory.putNumber(null,"555-2853");
System.out.println("Contents are:");
System.out.println();
directory.print();
System.out.println();
System.out.println("Number for Fred is " + directory.getNumber("Fred"));
System.out.println("Number for Wilma is " + directory.getNumber("Wilma"));
System.out.println("Number for Tom is " + directory.getNumber("Tom"));
System.out.println("Number for Tom is " + directory.getNumber("Alex"));
// The output from the last line should be null.
}
}
Output
This program creates a PhoneDirectoryWithTreeMap and
adds several entries; it then prints the contents of
the directory and performs a few lookups.
Contents are:
Barney: 555-2345
Fred: 555-1234
Wilma: 555-2563
Number for Fred is 555-1234
Number for Wilma is 555-2563
Number for Tom is null
Number for Tom is nullLast updated