How to write toString method to display name of Object

[Sandra Bachan]

Below code is a hybrid of Sierra/Bates Chapter 7, Question 4, and code from http://www.leepoint.net/notes-java/data/collections/maps/map_iteration.html

import java.util.*;
class MapEQ{
	public static void main(String[] args){
		Map<ToDos, String> m = new HashMap<ToDos, String>();
		ToDos t1 = new ToDos("Monday");
		ToDos t2 = new ToDos("Monday");
		ToDos t3 = new ToDos("Tuesday");
		m.put(t1, "doLaundry");
		m.put(t2, "payBills");
		m.put(t3, "cleanAttic");
		System.out.println(m.size());
		Iterator it = m.entrySet().iterator();
		while (it.hasNext()){
			Map.Entry pairs = (Map.Entry)it.next();
			System.out.println(pairs.getKey() + " = " + pairs.getValue());
		}
	}
}
class ToDos{
	String day;
	ToDos(String d){day = d;}
	public boolean equals(Object o){
		return ((ToDos)o).day == this.day;
	}
	//public int hashCode(){return 9;}
}

Output:

3
ToDos@12b6651 = doLaundry
ToDos@1888759 = cleanAttic
ToDos@4a5ab2 = payBills


From what I understand, if we implement hashCode, only two entries are in HashMap because Monday-payBills overwrites Monday-doLaundy, whereas if we leave it alone both doLaundry and payBills are present.

Question: How to write toString function so that it gives neat output, i.e.

3
t1 = doLaundry
t2 = cleanAttic
t3 = payBills

[Shanky Sohar]

but i am getting compiler error at these lines..........

 Iterator it = m.entrySet().iterator();   
        while (it.hasNext()){   
            Map.Entry pairs = (Map.Entry)it.next();   

[Minhaj Mehmood]

Sandra Bachan wrote:From what I understand, if we implement hashCode, only two entries are in HashMap because Monday-payBills overwrites Monday-doLaundy, whereas if we leave it alone both doLaundry and payBills are present.

Well it's because your implemented hashCode method is not well formed.

Sandra Bachan wrote:Question: How to write toString function so that it gives neat output, i.e.

3
t1 = doLaundry
t2 = cleanAttic
t3 = payBills

What I understand, you want to output like

3
Monday = doLaundry
Tuesday = cleanAttic
Monday = payBills

for above out put just edit your ToDos class as per following listed code:

class ToDos{
	String day;
	ToDos(String d){day = d;}
	public boolean equals(Object o){
		return ((ToDos)o).day == this.day;
	}

	public String toString(){
		return day;
	}
	//public int hashCode(){return 9;}
}

HTH

Minhaj

[Sandra Bachan]

phil sohar wrote:but i am getting compiler error at these lines..........

 Iterator it = m.entrySet().iterator();   
        while (it.hasNext()){   
            Map.Entry pairs = (Map.Entry)it.next();   

How are you compiling, i.e. if using command-line, what are you typing.

And what exactly is the error?

[Sandra Bachan]

Minhaj Mehmood wrote:
What I understand, you want to output like

3
Monday = doLaundry
Tuesday = cleanAttic
Monday = payBills

for above out put just edit your ToDos class as per following listed code:

class ToDos{
	String day;
	ToDos(String d){day = d;}
	public boolean equals(Object o){
		return ((ToDos)o).day == this.day;
	}

	public String toString(){
		return day;
	}
	//public int hashCode(){return 9;}
}

HTH

Minhaj

Thanks!

[Abimaran Kugathasan]

What toString() method does, describes the object meaningfully. If it's your job to describe your own object. So it can be a state, or some other, but it should differentiate the two object, otherwise, no meaning.

[Prasad Kharkar]

and also
toString() method on the object gets called when we try to print the object using println() printf() or the print() method
so we do not need to call that method explicitly