How to use the toString method in Java

Question

Can anybody explain to me the concept of the toString   method  defined in the Object class  How is it used  and what is its purpose

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From the Object toString docs      Returns a string representation of the   object  In general  the toString   method returns a string that    textually represents  this object    The result should be a concise but   informative representation that is   easy for a person to read  It is   recommended that all subclasses   override this method        The toString method for class Object   returns a string consisting of the   name of the class of which the object   is an instance  the at-sign character        and the unsigned hexadecimal   representation of the hash code of the   object  In other words  this method   returns a string equal to the value   of    getClass   getName           Integer toHexString hashCode      Example   String   mystr    a   b   c    System out println  mystr toString      mystr toString      output - mystr toString   Ljava lang String  13aaa14a

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If you learn Python first and then Java  I think it plays the same role as   str     method in Python  it is a magic method like   dict     and   init     but to refer to a string representing the the object

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Whenever you access an Object  not being a String  in a String context then the toString   is called under the covers by the compiler   This is why  Map map   new HashMap    System out println  map     map     works  and by overriding the standard toString   from Object in your own classes  you can make your objects useful in String contexts too    and consider it a black box   Never  ever use the contents for anything else than presenting to a human

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Use of the String toString   Whenever you require to explore the constructor called value in the String form  you can simply use String toString    for an example     package pack1   import java util     class Bank        String n      String add      int an      int bal      int dep       public Bank String n  String add  int an  int bal             this add   add          this bal   bal          this an   an          this n   n              public String toString             return  Name of the customer      this n                            Address of the customer      this add            A c no                       this an            Balance in A c       this bal           public class Demo2        public static void main String   args             List lt Bank gt  l   new LinkedList lt Bank gt              Bank b1   new Bank  naseem1    Darbhanga bihar   123  1000           Bank b2   new Bank  naseem2    patna bihar   124  1500           Bank b3   new Bank  naseem3    madhubani bihar   125  1600           Bank b4   new Bank  naseem4    samastipur bihar   126  1700           Bank b5   new Bank  naseem5    muzafferpur bihar   127  1800           l add b1           l add b2           l add b3           l add b4           l add b5           Iterator lt Bank gt  i   l iterator            while  i hasNext                  System out println i next                              copy this program into your Eclipse  and run it    you will get the ideas about String toString

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Coding     public class Test        public static void main String args               ArrayList lt Student gt  a   new ArrayList lt Student gt             a add new Student  Steve   12   Daniel             a add new Student  Sachin   10   Tendulkar              System out println a            display a               static void display ArrayList lt Student gt  stu             stu add new Student  Yuvi   12   Bhajji              System out println stu               Student java   public class Student        public String name       public int id       public String email       Student                 Student String name  int id  String email             this name   name          this id   id          this email   email               public String toString                using these toString to avoid the output like this  com steve test Student 6e1408  com steve test Student e53108            return name     id     email                          public String getName             return name             public void setName String name            this name name             public int getId             return id             public void setId int id            this id id             public String getEmail             return email              public void setEmail String email            this email email            Output       Steve 12 Daniel  Sachin 10 Tendulkar        Steve 12 Daniel  Sachin 10 Tendulkar  Yuvi 12 Bhajji    If you are not used toString   in Pojo Student java  class you will get an output like  com steve test Student 6e1408  com steve test Student e53108  To avoid these kind of issue we are using toString   method

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the toString   converts the specified object to a string value

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toString   returns a string textual representation of the object  Commonly used for diagnostic purposes like debugging  logging etc   the toString   method is used to read meaningful details about the object   It is automatically invoked when the object is passed to println  print  printf  String format    assert or the string concatenation operator   The default implementation of toString   in class Object returns a string consisting of the class name of this object followed by   sign and the unsigned hexadecimal representation of the hash code of this object using the following logic   getClass   getName           Integer toHexString hashCode      For example  the following  public final class Coordinates        private final double x      private final double y       public Coordinates double x  double y            this x   x          this y   y             public static void main String   args            Coordinates coordinates   new Coordinates 1  2           System out println  Bourne s current location -     coordinates             prints  Bourne s current location - Coordinates addbf1   concise  but not really useful to the reader   Now  overriding toString   in the Coordinates class as below    Override public String toString         return       x          y            results in  Bourne s current location -  1 0  2 0    concise and informative   The usefulness of overriding toString   becomes even more when the method is invoked on collections containing references to these objects  For example  the following  public static void main String   args        Coordinates bourneLocation   new Coordinates 90  0       Coordinates bondLocation   new Coordinates 45  90       Map lt String  Coordinates gt  locations   new HashMap lt String  Coordinates gt         locations put  Jason Bourne   bourneLocation       locations put  James Bond   bondLocation       System out println locations       prints   James Bond  45 0  90 0   Jason Bourne  90 0  0 0     instead of this    James Bond Coordinates addbf1  Jason Bourne Coordinates 42e816    Few implementation pointers    You should almost always override the toString   method  One of the cases where the override wouldn t be required is utility classes that group static utility methods  in the manner of java util Math  The case of override being not required is pretty intuitive  almost always you would know  The string returned should be concise and informative  ideally self-explanatory  At least  the fields used to establish equivalence between two different objects i e  the fields used in the equals   method implementation should be spit out by the toString   method  Provide accessors getters for all of the instance fields that are contained in the string returned  For example  in the Coordinates class   public double getX         return x    public double getY         return y       A comprehensive coverage of the toString   method is in Item 10 of the book  Effective Java     Second Edition  By Josh Bloch

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The toString   method returns a textual representation of an object  A basic implementation is already included in java lang Object and so because all objects inherit from java lang Object it is guaranteed that every object in Java has this method   Overriding the method is always a good idea  especially when it comes to debugging  because debuggers often show objects by the result of the toString   method  So use a meaningful implementation but use it for technical purposes  The application logic should use getters   public class Contact     private String firstName    private String lastName    public Contact  String firstName  String lastName        this firstName   firstName      this lastName   lastName        public String getFirstName    return firstName     public String getLastName    return lastName      public String getContact         return firstName         lastName          Override   public String toString         return     getContact

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It may optionally have uses within the context of an application but far more often it is used for debugging purposes  For example  when you hit a breakpoint in an IDE  it s far easier to read a meaningful toString   of objects than it is to inspect their members   There is no set requirement for what a toString   method should do  By convention  most often it will tell you the name of the class and the value of pertinent data members  More often than not  toString   methods are auto-generated in IDEs   Relying on particular output from a toString   method or parsing it within a program is a bad idea  Whatever you do  don t go down that route

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The main purpose of toString is to generate a String representation of an object  means the return value is always a String  In most cases this simply is the object s class and package name  but on some cases like StringBuilder you will got actually a String-text

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This toString-Method works for every Class  where you want to display all the fields and its values     public String toString          StringBuffer sb   new StringBuffer         Field   fields   getClass   getDeclaredFields      Get all fields incl  private ones      for  Field field   fields            try                field setAccessible true               String key field getName                String value               try                  value    String  field get this                 catch  ClassCastException e                   value                                sb append key  append       append value  append   n               catch  IllegalArgumentException e                e printStackTrace              catch  SecurityException e                e printStackTrace              catch  IllegalAccessException e                e printStackTrace                          return sb toString

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Apart from what cletus answered with regards to debugging  it is used whenever you output an object  like when you use   System out println myObject     or  System out println  text     myObject

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Correctly overridden toString method can help in logging and debugging of Java

[java] How to use the toString method in Java?

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