CODEWITHSUNDEEP
java
user1283885
user1283885

Reputation: 1263

How to override toString() properly in Java?

Sounds a little stupid, but I need help on my toString() method and it is very irking. I tried looking up online because the toString is the one where it is screwing up and "not finding Kid constructor #2" even though it is there and I would even do something else and it doesn't work. Ok that was a lot so here is my code: 

import java.util.*; 
   class Kid {  
      String name; 
      double height; 
      GregorianCalendar bDay; 

      public Kid () { 
         this.name = "HEAD";
         this.height = 1; 
         this.bDay = new GregorianCalendar(1111,1,1); 
      } 

      public Kid (String n, double h, String date) {
      // method that toString() can't find somehow
         StringTokenizer st = new StringTokenizer(date, "/", true);
         n = this.name;
         h = this.height;
      } 

      public String toString() { 
         return Kid(this.name, this.height, this.bDay);
      } 
   } //end class

Ok So my toString above (I know, my third parameter is off, should be a String) is off. If I hardcode a value in for the third thing it goes haywire and says it can't find this (up above). So how can I get the date and break it up?

Class calling this is below

class Driver {   
   public static void main (String[] args) {   
      Kid kid1 = new Kid("Lexie", 2.6, "11/5/2009");   
      System.out.println(kid1.toString());
   } //end main method 
} //end class

I tried researching multiple constructors and it really didn't help. I tried researching toString() methods, and tried using previous toString() methods logic that I created previous but this is brand new so it never worked.

Help?

Upvotes: 104

Views: 378844

Answers (15)

Anil Bishnoi
Anil Bishnoi

Reputation: 24

But then in the toString() method you aren't actually returning a String, are you? You'll have to return a String for this method to work.

public String toString() {
  return "Name : " + this.name + " Height : " + this.height + " BirthDay : " + this.bday;
}

Upvotes: 0

Basil Bourque
Basil Bourque

Reputation: 339858

As others explained, the toString is not the place to be instantiating your class. Instead, the toString method is intended to build a string representing the value of an instance of your class, reporting on at least the most important fields of data stored in that object. In most cases, toString is used for debugging and logging, not for your business logic (except some historical methods, like Integer.toString()).

To generate text representing the value of an object for display to a user, add another method. People often name the method something like getDisplayName. For example, DayOfWeek::getDisplayName and Month::getDisplayName.

StringJoiner

As of Java 8 and later, the most modern way to implement toString would use the StringJoiner class. As the doc says:

StringJoiner is used to construct a sequence of characters separated by a delimiter and optionally starting with a supplied prefix and ending with a supplied suffix.

Use like this:

@Override
public String toString ()
{
    return new StringJoiner(                           // In Java 8 and later, StringJoiner is used to construct a sequence of characters separated by a delimiter and optionally starting with a supplied prefix and ending with a supplied suffix.
                " | " ,                                // Delimiter
                Person.class.getSimpleName() + "[ " ,  // Prefix
                " ]"                                   // Suffix
            )
            .add( "name=" + name )                     // Append
            .add( "phone=" + phone )                   // Append
            .toString();                               // Convert entire sequence to a single `String` object.
}

Person[ name=Alice | phone=555.867.5309 ]

record

Java 16 brings a new way to briefly define a class where the main purpose is to communicate data transparently and immutably: record.

You define a record by merely listing the type and name of each member field. The compiler implicitly creates the constructor, getters, equals & hashCode, and toString.

Default implementation of toString

The default implementation of toString includes each and every member field.

public Kid ( String name , double height , LocalDate birthDate ) {}

Instantiate like any other object.

Kid alice = new Kid( "Alice" , 6.1d , LocalDate.of( 2019 , Month.April , 23 ) ) ;
String output = alice.toString() ;

You may choose to override the default implementation with your own. Overrides are usually not needed given the purpose of a record as a simple data-carrier.

Upvotes: 13

logbasex
logbasex

Reputation: 2312

Always have easy way: Right Click > Generate > toString() > select template that you want. enter image description here

Upvotes: 1

Brent Bradburn
Brent Bradburn

Reputation: 54979

If you're just using toString() for debugging a DTO, you can generate human readable output automatically with something like the following: 

import com.fasterxml.jackson.databind.ObjectMapper;
...
public String toString() {
    try { return new ObjectMapper().writeValueAsString(this); }
    catch (Exception e) { return "{ObjectMapper failed}"; }
}

However, this isn't appropriate for production deployments if the DTO may contain PII (which shouldn't be captured in logs).

Upvotes: 1

stinger
stinger

Reputation: 4146

Nice and concise way is to use Lombok annotations. It has @ToString annotation, which will generate an implementation of the toString() method. By default, it will print your class name, along with each field, in order, separated by commas. You can easily customize your output by passing parameters to annotation, e.g.:

@ToString(of = {"name", "lastName"})

Which is equivalent of pure Java:

public String toString() {
        return "Person(name=" + this.name + ", lastName=" + this.experienceInYears + ")";
    }

Upvotes: 1

The Guy
The Guy

Reputation: 421

  1. if you are use using notepad: then 

    public String toString(){

 return ""; ---now here you can use variables which you have created for your class

}

  2. if you are using eclipse IDE then press

    -alt +shift +s

    -click on override toString method here you will get options to select what type of variables you want to select.

Upvotes: 0

user666
user666

Reputation: 2013

The best way in my opinion is using google gson library:

        @Override
public String toString() {
    return new GsonBuilder().setPrettyPrinting().create().toJson(this);
}

or apache commons lang reflection way

Upvotes: 3

granadaCoder
granadaCoder

Reputation: 27904

If you're interested in Unit-Tests, then you can declare a public "ToStringTemplate", and then you can unit test your toString. Even if you don't unit-test it, I think its "cleaner" and uses String.format.

public class Kid {

    public static final String ToStringTemplate = "KidName='%1s', Height='%2s', GregCalendar='%3s'";

    private String kidName;
    private double height;
    private GregorianCalendar gregCalendar;

    public String getKidName() {
        return kidName;
    }

    public void setKidName(String kidName) {
        this.kidName = kidName;
    }

    public double getHeight() {
        return height;
    }

    public void setHeight(double height) {
        this.height = height;
    }

    public GregorianCalendar getGregCalendar() {
        return gregCalendar;
    }

    public void setGregCalendar(GregorianCalendar gregCalendar) {
        this.gregCalendar = gregCalendar;
    }

    public String toString() { 
        return String.format(ToStringTemplate, this.getKidName(), this.getHeight(), this.getGregCalendar());
    } 
}

Now you can unit test by create the Kid, setting the properties, and doing your own string.format on the ToStringTemplate and comparing.

making ToStringTemplate static-final means "ONE VERSION" of the truth, rather than having a "copy" of the template in the unit-test.

Upvotes: 2

sudmong
sudmong

Reputation: 2036

You can creating new object in the toString(). use

return "Name = " + this.name +" height= " + this.height;

instead of 

return Kid(this.name, this.height, this.bDay);

You may change the return string as required. There are other ways to store date instead calander.

Upvotes: 4

user7321815
user7321815

Reputation: 11

we can even write like this by creating a new String object in the class and assigning it what ever we want in constructor and return that in toString method which is overridden

public class Student{  
 int id;  
 String name;  
 String address;  
 String details;
 Student(int id, String name, String address){  
 this.id=id;  
 this.name=name;  
 this.address=address;  
 this.details=id+"  "+name+"  "+address;  
 }  

//overriding the toString() method  
public String toString(){ 
  return details;  
 }  
 public static void main(String args[]){  
   Student s1=new Student(100,"Joe","success");  
   Student s2=new Student(50,"Jeff","fail");  

   System.out.println(s1);//compiler writes here s1.toString()  
   System.out.println(s2);//compiler writes here s2.toString()  
 }  
}

Upvotes: 1

Mohamed Sherif Noureldin
Mohamed Sherif Noureldin

Reputation: 430

Well actually you will need to return something like this because toString has to return a string

public String toString() {
 return "Name :" + this.name + "whatever :" + this.whatever + "";
}

and you actually do something wrong in the constructer you set the variable the user set to the name while you need to do the opposite. What you shouldn't do

n = this.name

What you should do

this.name = n

Hopes this helps thanks

Upvotes: 1

Linux Le
Linux Le

Reputation: 456

Java toString() method

If you want to represent any object as a string, toString() method comes into existence.

The toString() method returns the string representation of the object.

If you print any object, java compiler internally invokes the toString() method on the object. So overriding the toString() method, returns the desired output, it can be the state of an object etc. depends on your implementation.

Advantage of Java toString() method

By overriding the toString() method of the Object class, we can return values of the object, so we don't need to write much code.

Output without toString() method

class Student{  
 int id;  
 String name;  
 String address;  

 Student(int id, String name, String address){  
 this.id=id;  
 this.name=name;  
 this.address=address;  
 }  

 public static void main(String args[]){  
   Student s1=new Student(100,”Joe”,”success”);  
   Student s2=new Student(50,”Jeff”,”fail”);  

   System.out.println(s1);//compiler writes here s1.toString()  
   System.out.println(s2);//compiler writes here s2.toString()  
 }  
}  

Output:Student@2kaa9dc
       Student@4bbc148

You can see in the above example #1. printing s1 and s2 prints the Hashcode values of the objects but I want to print the values of these objects. Since java compiler internally calls toString() method, overriding this method will return the specified values. Let's understand it with the example given below:

Example#2

Output with overriding toString() method

class Student{  
 int id;  
 String name;  
 String address;  

 Student(int id, String name, String address){  
 this.id=id;  
 this.name=name;  
 this.address=address;  
 }  

//overriding the toString() method  
public String toString(){ 
  return id+" "+name+" "+address;  
 }  
 public static void main(String args[]){  
   Student s1=new Student(100,”Joe”,”success”);  
   Student s2=new Student(50,”Jeff”,”fail”);  

   System.out.println(s1);//compiler writes here s1.toString()  
   System.out.println(s2);//compiler writes here s2.toString()  
 }  
} 

Output:100 Joe success
       50 Jeff fail

Note that toString() mostly is related to the concept of polymorphism in Java. In, Eclipse, try to click on toString() and right click on it.Then, click on Open Declaration and see where the Superclass toString() comes from.

Upvotes: 17

RCR
RCR

Reputation: 539

Following code is a sample. Question based on the same, instead of using IDE based conversion, is there a faster way to implement so that in future the changes occur, we do not need to modify the values over and over again?

@Override
    public String toString() {
        return "ContractDTO{" +
                "contractId='" + contractId + '\'' +
                ", contractTemplateId='" + contractTemplateId + '\'' +
                '}';
    }

Upvotes: 3

Adrian Pronk
Adrian Pronk

Reputation: 13926

You can't call a constructor as if it was a normal method, you can only call it with new to create a new object:

Kid newKid = new Kid(this.name, this.height, this.bDay);

But constructing a new object from your toString() method is not what you want to be doing.

Upvotes: 3

adarshr
adarshr

Reputation: 62603

The toString is supposed to return a String.

public String toString() { 
    return "Name: '" + this.name + "', Height: '" + this.height + "', Birthday: '" + this.bDay + "'";
}

I suggest you make use of your IDE's features to generate the toString method. Don't hand-code it.

For instance, Eclipse can do so if you simply right-click on the source code and select Source > Generate toString

Upvotes: 154

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