Java Constructor instances not reading input [duplicate]

Question

I have just started learning java and I was given a pretty simple assignment on constructors and instances. For some reason my instances are not being set when they are created and only when I call the set methods. Can you please help me out I've been stuck for a while now with no where to go.

package hka437documents;

/**
*
* @author Henry
*/
public class Hka437Documents{

    public static class Documents {
    /**
    * @param args the command line arguments
    */ 
        private String title;
        private String author;
        private String body;
        private int version;

        public Documents(String title, String author){
            version = 0;
        }
        public Documents(String title, String author, String body){
            version = 1;
        }

        public void setTitle(String title){
            this.title = title;
            version++;
        }        
        public void setAuthor(String author){
            this.author = author;
        }
        public void setBody(String body){
            this.body = body;
            version++;
        }
        public String getTitle(){
            return title;
        }
        public String getAuthor(){
            return author;
        }
        public String getBody(){
            return body;
        }
        public int getVersion(){
            return version;
        }
    } 
    public static void main(String[] args) {

        Documents document1 = new Documents("Another Life", "Sally Smith");
        document1.setBody("The grass is always greener on the other side.");

        Documents document2 = new Documents("Final Word", "Karen Jones", "We should plan for the worst and hope for the best.");
        document2.setTitle("Final Words");

        System.out.println("document1:");
        System.out.println("Title: "+ document1.getTitle());
        System.out.println("Author: "+ document1.getAuthor());
        System.out.println("Body: "+ document1.getBody());
        System.out.println("Version: "+ document1.getVersion());
        System.out.println("\ndocument2:");
        System.out.println("Title: "+ document2.getTitle());
        System.out.println("Author: "+ document2.getAuthor());
        System.out.println("Body: "+ document2.getBody());
        System.out.println("Version: "+ document2.getVersion());
        }  
}

When I run the program I get null on the print statements for all of them except for the document1+2 version, document1 body and document2 title. These are the ones that had variables set with the set methods.

You're doing nothing with your constructor parameters. They're not going to change the state of the object by magic -- you need to assign their value to state fields of your object. — Hovercraft Full Of Eels
– Hovercraft Full Of Eels, Commented Feb 10, 2016 at 3:58
Downvoter care to comment? Yes, it's a beginner question but it contains the required elements (code, explanation of what's not working). We were all newbies at some point, at least this newbie knows how to ask a question. — Jim Garrison
– Jim Garrison, Commented Feb 10, 2016 at 4:00

Martín Muñoz del Río · Accepted Answer · 2016-02-10 04:00:09Z

0

Look here:

    public Documents(String title, String author){
        version = 0;
    }
    public Documents(String title, String author, String body){
        version = 1;
    }

Your constructors only initialize version.

You have to add:

this.title = title;
this.author = author;

in the first, and:

this.title = title;
this.author = author;
this.body = body;

In the second.

answered Feb 10, 2016 at 4:00

Martín Muñoz del Río

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Comments

Pablo · Accepted Answer · 2016-02-10 04:00:20Z

0

you have to set atributes with params values in the constructor:

public Documents(String title, String author){
            version = 0;
            this.title = title;
            this.author = author; 
        }
public Documents(String title, String author, String body){
            version = 1;
            this.title = title;
            this.author = author;
            this.body= body;
        }

answered Feb 10, 2016 at 4:00

Pablo

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9 Comments

Mihado Over a year ago

He will also need an implicit constructor for it to work Documents();

user207421 Over a year ago

@Mihado He will need that why? He's not using it anywhere.

Mihado Over a year ago

He will get a compiler error. You can't have explicit constructors without an implicit default one.

Pablo Over a year ago

Yes, you can and it won't give a compiler error

Pablo Over a year ago

Please, see the first example on this oracle doc about java clases docs.oracle.com/javase/tutorial/java/javaOO/classes.html

|

HTNW · Accepted Answer · 2016-02-10 04:02:02Z

0

You actually want to set the fields in the constructor, they won't just be copied by magic. Right now they are just being ignored. You'd want a change like the following in both constructors:

this.title = title;
this.author = author;

You also want something similar to set body as well.

this.body = body;

answered Feb 10, 2016 at 4:02

HTNW

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