hashmapexample.java

来自「java 完全探索的随书源码」· Java 代码 · 共 54 行

import java.util.HashMap;

public class HashMapExample {

  public void doExample() {
    HashMap myMap = new HashMap(2);

    Employee emp = new Employee( "123-45-6789", "Smith", "John" );
    myMap.put( emp.getSocialSecurityNumber(), emp );
    emp = new Employee( "987-65-4321", "Doe", "Jane" );
    myMap.put( emp.getSocialSecurityNumber(), emp );

    if ( myMap.containsKey("123-45-6789") ) {
      System.out.println("Found by key: " + myMap.get("123-45-6789"));
    }

    if ( myMap.containsValue(emp) ) {
      System.out.println("Map contains value: " +
        myMap.get(emp.getSocialSecurityNumber()));
    }

    // clear the list and verify that it's empty
    myMap.clear();
    System.out.println("Map is now " +
      (myMap.isEmpty() ? "Empty" : "Not Empty"));
  }

  public static void main( String args[] ) {
    new HashMapExample().doExample();
  }
}

class Employee {
  private String socialSecurityNumber;
  private String lastName;
  private String firstName;

  public Employee( String ssn, String lname, String fname ) {
    socialSecurityNumber = ssn;
    lastName = lname;
    firstName = fname;
  }

  // the SSN can be retrieved, but is immutable, which
  // is best for an object used as a key
  public String getSocialSecurityNumber() {
    return socialSecurityNumber;
  }

  public String toString() {
    return socialSecurityNumber + " " + lastName + ", " + firstName;
  }
}