HashMaps

[Rao.K Reddy]

Hi guys, I need help regarding my assignment...i am beginner in Java....my query is like: "i want to create hashmaps where the inner hashmap contains the key as firstname and value as a Class Student which contains parameters firstname, lastname,etc. I need this hashmap to be accessed by other objects of different classes". Please, help me out?

public class Student {
	
	private String FirstName;
	private String LastName;
	private String EmailAddress;
	private String PhoneNumber;
	private String Username;
	private String Password;
	private String EducationalInstitution;
	
	public Student(String firstname,
           String lastname,String email,String phno,
           String user,String pass,String edu)	
	{	
	  FirstName=firstname;
	  LastName=lastname;
	  EmailAddress=email;
	  PhoneNumber=phno;
	  Username=user;
	  Password=pass;
	  EducationalInstitution=edu;  
	}
		
	public Student() {
		super();
		// TODO Auto-generated constructor stub
	}

	public String getFirstName() {
		return FirstName;
	}
	public void setFirstname(String firstname) {
		FirstName = firstname;
	}
	public String getLastName() {
		return LastName;
	}
	public void setLastName(String lastname) {
		LastName = lastname;
	}
	public String getEmailAddress() {
		return EmailAddress;
	}
	public void setEmailAdress(String email) {
		EmailAddress = email;
	}
	public String getPhoneNumber() {
		return PhoneNumber;
	}
	public void setPhoneNumber(String phoneNumber) {
		PhoneNumber = phoneNumber;
	}
	public String getUsername() {
		return Username;
	}
	public void setUsername(String username) {
		Username = username;
	}
	public String getPassword() {
		return Password;
	}
	public void setPassword(String password) {
		Password = password;
	}
	public String getEducationalInstitution() {
		return EducationalInstitution;
	}
	public void setEducationalInstitution(String educationalInstitution) {
		EducationalInstitution = educationalInstitution;
	}
	public String toString(){
		return "Student [FirstName="+FirstName+
                     ",LastName="+LastName+",EmailAddress="+EmailAddress+
                     ",PhoneNumber="+PhoneNumber+",EducationalInstitution="+
                     EducationalInstitution+")";
	}

}

Here I have a main class

public class StudentInfo {

	public static void main(String args[]) 
	{ 
		String FirstName; 
		String LastName; 
		String EmailAddress; 
		String PhoneNumber; 
		String Username;
		String Password;
		String EducationalInstitution;

        Scanner input=new Scanner(System.in)
	Map<String,Student>> map=new HashMap<String,Student>();

	System.out.print("Enter FirstName  "); 
	FirstName = in.nextLine(); 
	System.out.print("Enter LastName  "); 
	LastName = in.nextLine(); 
	System.out.print("Enter EmailAddress "); 
	EmailAddress = in.nextLine(); 
	System.out.print("Enter PhoneNumber "); 
	PhoneNumber = in.nextLine(); 
	System.out.print("Enter Username "); 
	Username = in.nextLine(); 
	System.out.print("Enter Password "); 
	Password = in.nextLine(); 
	System.out.println("Enter Educational Institution:");
	EducationalInstitution = in.nextLine();

As we give the values by Scanner, it should be Stored in Hashmap and how those values can be accessed by other object classes?
How does the Logic works? What my next step?

[Dave Tolls]

You need to take those values and create a Student instance. There's a suitable constructor on Student that allows you to do this.
Then you need to put the Student (and Key) into the Map, using a suitable method on the java.util.Map API (there's a hint in this sentence in fact).

One thing, the standard Java code style is that classes start with a Capital (which you do, which is great), but variables start with a lower case. This makes it easier for people to spot whether something in the code is referring to a class or a variable,

[Campbell Ritchie]

Please check the formatting of the code. You have fields starting with CapitalLetters (should be capitalLetters for a field), which can under certain circumstances cause logic errors or even compiler errors.
You have insufficient spacing between tokens and your lines are too long. I have broken the long lines so you can see how to do it.
Sorting out those thing swill make your code easier to understand and make it easier to read and will get you better marks

[Rao.K Reddy]

I dont want to declare key and values as an object

Student st1=new Student("fname","lname","email","phno","user","passwd","eduIns")
Student st2=new Student("fname2","lname2","email2","phno2","user2","passwd2","eduIns")
...
...
...
...
System.out.println(st1);
System.out.println(st2);
...
...
...

instead i want to use scanner to input the values into hashmap...how to do it?

[Carey Brown]

Your requirements are a bit vague and it's hard to know what you're really shooting for, but here's a stab at it.

private static final String[]	fields =
{
"FirstName",
"LastName",
"EmailAddress",
"PhoneNumber",
"Username",
"Password",
"EducationalInstitution"
};


public static void main( String... args )
{
Map<String,Map<String,String>> outerMap = new HashMap<String,Map<String,String>>();

for( int i=0 ; i < numberOfStudents ; i++ )
{
    Map<String,String> innerMap  = new HashMap<String,String>();
    for( String field : fields )
    {
        System.out.print( "Enter " + field );
        String s = in.nextLine();
        innerMap.put( field, s );
    }
   outerMap.put( innerMap.getValue( "FirstName" ), innerMap );
}

[Rao.K Reddy]

hey Caren the code you mentioned isn't working ...m getting an error: " getValue() method doesn't exist " ...

[Winston Gutkowski]

Carey Brown wrote:Your requirements are a bit vague and it's hard to know what you're really shooting for, but here's a stab at it...

I like your method of getting the data - ie, an array of field names - but not your final structure. You might want to read the StringsAreBad page to find out why.

Personally, I'd say there are at least two types in play here: a Student, and a User. Now in many cases they may refer to the same person, but that doesn't necessarily mean they're the same thing. A User could possibly also be a teacher, or an admin; and I doubt that a Student can't exist without being a User of the system.

Just a few of the things you need to consider when thinking about types (or classes).

HIH

Winston

[Carey Brown]

Winston Gutkowski wrote:

Carey Brown wrote:Your requirements are a bit vague and it's hard to know what you're really shooting for, but here's a stab at it...

I like your method of getting the data - ie, an array of field names - but not your final structure. You might want to read the StringsAreBad page to find out why.

Personally, I'd say there are at least two types in play here: a Student, and a User. Now in many cases they may refer to the same person, but that doesn't necessarily mean they're the same thing. A User could possibly also be a teacher, or an admin; and I doubt that a Student can't exist without being a User of the system.

Just a few of the things you need to consider when thinking about types (or classes).

HIH

Winston

Sorry, getValue() should have been get(). I just threw it together with notepad and didn't check it. I know strings are not a good way to add structure but it seemed like that was what the OP was looking for as other suggestions were not what he wanted.