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?
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
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<Bank> l = new LinkedList<Bank>();
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<Bank> 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...
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()+"]";
}
}
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.
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<String, Coordinates> locations = new HashMap<String, Coordinates>();
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.
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)
Correctly overridden toString method can help in logging and debugging of Java.
Coding:
public class Test {
public static void main(String args[]) {
ArrayList<Student> a = new ArrayList<Student>();
a.add(new Student("Steve", 12, "Daniel"));
a.add(new Student("Sachin", 10, "Tendulkar"));
System.out.println(a);
display(a);
}
static void display(ArrayList<Student> 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.
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);
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.
/**
* 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();
}
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.
the toString() converts the specified object to a string value.
I'm iterating over a ResultSet and save it to a ArrayList.
weatherData = Arrays.asList (
new WeatherInfo(rs.getDate(1), rs.getInt(2)...
When I do a System.out.println(weatherData); I see this in the Eclipse Console:
[com.example.project.view.ChartsData$WeatherInfo#66ee6cea, com.example.project.view.ChartsData$WeatherInfo#757d0531.....
What does it mean? Is it a value I can handle in Java or not?
Is this the actual date and int that I can use in Java?
thanks
You need to override toString() method in WeatherInfo class. What you see is its default implementation that presents its memory location.
This is a typical model object in Java with a toString() method. I used Intellij Idea (recommended!) which has the ability to auto-generate toString() and other methods such as equals() and hashCode(). We find that having these methods on all model objects is very useful for debugging and testing.
Running main() will output:
weatherInfo = WeatherInfo{country='CA', probablyOfPrecipitation=20}
public class WeatherInfo {
public static void main(String [] args) {
WeatherInfo weatherInfo = new WeatherInfo();
weatherInfo.setCountry("CA");
weatherInfo.setProbablyOfPrecipitation(20);
System.out.println("weatherInfo = " + weatherInfo);
}
String country;
int probablyOfPrecipitation;
public String getCountry() {
return country;
}
public void setCountry(String country) {
this.country = country;
}
public int getProbablyOfPrecipitation() {
return probablyOfPrecipitation;
}
public void setProbablyOfPrecipitation(int probablyOfPrecipitation) {
this.probablyOfPrecipitation = probablyOfPrecipitation;
}
#Override
public String toString() {
return "WeatherInfo{" +
"country='" + country + '\'' +
", probablyOfPrecipitation=" + probablyOfPrecipitation +
'}';
}
}
Top Tip!
We use a library called EqualsVerifier to guarantee that all equals() and hashCode() implementations are correct.
Hello all I am new in java.Please help me
I have following code
package sun.mun.fun;
import inship.InShipException;
import inship.PackageDetail;
import inship.Uspsrates;
import inship.UspsratesAboutPropertyEditor;
import inship.UspsratesBeanInfo;
import inship.UspsratesRequestedServicePropertyEditor;
public class Usps {
public Uspsrates getRate() {
Uspsrates rate = new Uspsrates();
try {
rate.getUSPSAccount().setServer(rate.toString());
rate.getUSPSAccount().setServer("http://production.shippingapis.com/ShippingAPI.dll");
rate.getUSPSAccount().setUserId("747THEFI1034");
rate.getUSPSAccount().setPassword("510QU40FX616");
rate.getSenderAddress().setZipCode("27502");
rate.getRecipientAddress().setZipCode("20770");
rate.getPackages().add(new PackageDetail());
rate.getPackages().item(0).setWeight("1");
rate.getPackages().item(0).setLength(Integer.parseInt("5"));
rate.getPackages().item(0).setWidth(Integer.parseInt("5"));
rate.getPackages().item(0).setHeight(Integer.parseInt("5"));
rate.getPackages().item(0).setGirth((2 * rate.getPackages().item(0).getLength()) + (2 * rate.getPackages().item(0).getWidth()));
rate.getPackages().item(0).setSize(Integer.parseInt("0"));
rate.getPackages().item(0).setPackagingType(inship.PackageDetail.ptNone);
rate.setRequestedService(inship.Uspsrates.stUnspecified);
rate.getRates();
} catch (InShipException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return rate;
}
#Override
public String toString() {
return "Usps [getRate()=" + getRate() + "]";
}
public static void main(String[] args) {
Usps u = new Usps();
System.out.println(u.getRate().toString());
}
}
and when I run this it gives this output
inship.Uspsrates#16672d6
I don't want this value.I want this in string.What should i do any help.
Thanks in advance
Uspsrates class should override toString() method and should return a String with the details you want.If you simply print an Object,the compiler converts it into Object.toString() and returns a String in the following format ClassName#Hashcode
Check the documentation for the Object's to String method here
Move your toString() implementation to your Uspsrates object.
#Override
public String toString() {
return "Usps [getRate()=" + getRate() + "]";
}
Because your getRate() method returns a Uspsrates not Usps
gives this output inship.Uspsrates#16672d6
what else do you expect it should give you
Your toString() is inside the Usps class but your getRate() method returns an Object of type Uspsrates
When you are doing this
System.out.println(u.getRate().toString());
It is just printing the hash of the object returned by getRate()
How to fix this?
Just add a toString() inside your Uspsrates class
Here is an example of what I am trying to ask
superclass Name.java
public class Name{
protected String first;
protected String last;
public Name(String firstName, String lastName){
this.first = firstName;
this.last = lastName;
}
public String initials(){
String theInitials =
first.substring(0, 1) + ". " +
last.substring(0, 1) + ".";
return theInitials;
}
and then the subclass is ThreeNames.java
public class ThreeNames extends Name{
private String middle;
public ThreeNames(String aFirst, String aMiddle, String aLast){
super(aFirst, aLast);
this.middle = aMiddle;
}
public String initials(){
String theInitials =
super.first.substring(0, 1) + ". " +
middle.substring(0, 1) + ". " +
super.last.substring(0, 1) + ".";
return theInitials;
}
so if i create an Threename object with ThreeNames example1 = new ThreeNames("Bobby", "Sue" "Smith") and then call System.out.println(example1.initials()); I will get B.S.S. I get that.
My question is is there a way to call the initials method that is in the Name class so that my output is just B.S.
no. once you've overridden a method then any invocation of that method from outside will be routed to your overridden method (except of course if its overridden again further down the inheritance chain).
you can only call the super method from inside your own overridden method like so:
public String someMethod() {
String superResult = super.someMethod();
// go on from here
}
but thats not what youre looking for here.
you could maybe turn your method into:
public List<String> getNameAbbreviations() {
//return a list with a single element
}
and then in the subclass do this:
public List<String> getNameAbbreviations() {
List fromSuper = super.getNameAbbreviations();
//add the 3 letter variant and return the list
}
There are many ways to do it. One way: don't override Names#initials() in ThreeNames.
Another way is to add a method to ThreeNames which delegates to Names#initials().
public class ThreeNames extends Name {
// snip...
public String basicInitials() {
return super.initials();
}
}
I would instead leave initials alone in the superclass and introduce a new method that will return the complete initials. So in your code I would simply rename the initials method in ThreeNames to something else. This way your initials method is the same across the implementations of Name