CODEWITHSUNDEEP
javaloops
joewinfield91
joewinfield91

Reputation: 1

How to leave out a null value in a loop in Java

Here's my Java Code:

public class DVD {
    public static void main(String[] args) {
        DVD newdvd1 = new DVD();

        newdvd1.setPlayit("The song is playing \n");
        newdvd1.setArtist("Eva Cassidy");
        newdvd1.setTitle("Songbird");
        newdvd1.setGenre("Blues");

        System.out.println(newdvd1.getPlayit());
        System.out.println(newdvd1);

        DVD newdvd2 = new DVD();

        newdvd2.setPlayit("The next song is playing \n");
        newdvd2.setArtist("an unknown artist");
        newdvd2.setTitle("new song");

        System.out.println(newdvd2.getPlayit());
        System.out.println(newdvd2);
    }

    private String artist;
    private String title;
    private String genre;
    private String playit;

    public String getPlayit() {
        return playit;
    }
    public void setPlayit(String playit) {
        this.playit = playit;
    }
    public String getArtist() {
        return artist;
    }
    public void setArtist(String artist) {
        this.artist = artist;
    }
    public String getTitle() {
        return title;
    }
    public void setTitle(String title) {
        this.title = title;
    }
    public String getGenre() {
        return genre;
    }
    public void setGenre(String genre) {
        this.genre = genre; 
    }

    public String toString () {

        return ("The artist is called " + artist + 
            " who is a "+ genre + " singer" +
            " and this song is called " + title + ".\n");
    }
}

what it outputs is:

The song is playing 
The artist is called Eva Cassidy who is a Blues singer and this song is called Songbird.
The next song is playing 
The artist is called an unknown artist who is a null singer and this song is called new song.

What i'm asking is, in the second song, how do i leave out 'null singer' as I don't want to display the second songs genre?

Upvotes: 0

Views: 114

Answers (6)

gaborsch
gaborsch

Reputation: 15758

Use the ?: (ternary) operator. See JLS specs, for example. 

                 return ("The artist" +
                    (artist == null ? "" : " is called " + artist) +
                    (genre == null ? "" : " who is a "+ genre + " singer") +
                    (title == null ? "" : " and this song is called " + title) +
                     ".\n");

If the given property is not null, you print the relevant text, otherwise simply print nothing.

You can also define sensible default values like:

                    (artist == null ? " is unknown" : "is called " + artist) +

Upvotes: 2

NFoerster
NFoerster

Reputation: 416

You can insert a null check to skip this part. Anyway you should use a StringBuffer for that otherwise you are creating many String objects and make the GC angry. Every + creates a new String Object, so with a StringBuffer you only create one String at the end.

public String toString () 
{
    StringBuffer buffer = new StringBuffer("The artist is called ");
    buffer.append(artist);
    if(genre != null)
    {
        buffer.append(" who is a ");
        buffer.append(genre);
        buffer.append(" singer");
    }
    buffer.append(" and this song is called ");
    buffer.append(title);
    buffer.append(".\n");
    return buffer.toString();
}

Upvotes: 0

Robert
Robert

Reputation: 1316

If its just about the singer, you could do the following:

public String toString() {
    String temp = "The artist is called " + artist";
            if(singer != null){ //checks if the object "singer" is not null
                temp+=" who is a " + genre + " singer";
            }
    temp+="and this song is called "+ title + ".\n";
    return temp;
}

Upvotes: 0

Vinay Veluri
Vinay Veluri

Reputation: 6865

You can try this.

public String toString() {
    StringBuilder builder = new StringBuilder();

    if (artist != null && !artist.isEmpty()) {
        builder.append("The artist is called : " + artist);
    }

    if (genre != null && !genre.isEmpty()) {
        builder.append(" who is a " + genre + " singer");
    }
    if (title != null && !title.isEmpty()) {
        builder.append(" and this song is called " + title + ".\n");
    }

    return (builder.toString());
}

Upvotes: 1

Ruchira Gayan Ranaweera
Ruchira Gayan Ranaweera

Reputation: 35577

You should override toString() using some condition

public String toString () {
 if(genre!=null){
  return ("The artist is called " + artist + 
                    " who is a "+ genre + " singer" +
                    " and this song is called " + title + ".\n");
  }else{
   return ("The artist is called " + artist +
                 " and this song is called " + title + ".\n");          
   }

}

Upvotes: 0

Juned Ahsan
Juned Ahsan

Reputation: 68715

If you want the solution to be generic for then modify your toString method as:

         public String toString () {
            String returnString = "The artist is called " + artist ;

            if(genre !=null && !"".equals(genre.trim())) {
                returnString += " who is a "+ genre + " singer" +;
            }

            returnString +=  " and this song is called " + title + ".\n";
            return returnString;
         }

You can add more null checks if required for artist and title as well.

Upvotes: 0

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