Hashset to string [duplicate] - loops

I have a class defined as follows:
public class Person {
private String name;
// constructor and getter/setter omitted
}
I tried to print an instance of my class:
System.out.println(myPerson);
but I got the following output: com.foo.Person#2f92e0f4.
A similar thing happened when I tried to print an array of Person objects:
Person[] people = //...
System.out.println(people);
I got the output: [Lcom.foo.Person;#28a418fc
What does this output mean? How do I change this output so it contains the name of my person? And how do I print collections of my objects?
Note: this is intended as a canonical Q&A about this subject.

Background
All Java objects have a toString() method, which is invoked when you try to print the object.
System.out.println(myObject); // invokes myObject.toString()
This method is defined in the Object class (the superclass of all Java objects). The Object.toString() method returns a fairly ugly looking string, composed of the name of the class, an # symbol and the hashcode of the object in hexadecimal. The code for this looks like:
// Code of Object.toString()
public String toString() {
return getClass().getName() + "#" + Integer.toHexString(hashCode());
}
A result such as com.foo.MyType#2f92e0f4 can therefore be explained as:
com.foo.MyType - the name of the class, i.e. the class is MyType in the package com.foo.
# - joins the string together
2f92e0f4 the hashcode of the object.
The name of array classes look a little different, which is explained well in the Javadocs for Class.getName(). For instance, [Ljava.lang.String means:
[ - an single-dimensional array (as opposed to [[ or [[[ etc.)
L - the array contains a class or interface
java.lang.String - the type of objects in the array
Customizing the Output
To print something different when you call System.out.println(myObject), you must override the toString() method in your own class. Here's a simple example:
public class Person {
private String name;
// constructors and other methods omitted
#Override
public String toString() {
return name;
}
}
Now if we print a Person, we see their name rather than com.foo.Person#12345678.
Bear in mind that toString() is just one way for an object to be converted to a string. Typically this output should fully describe your object in a clear and concise manner. A better toString() for our Person class might be:
#Override
public String toString() {
return getClass().getSimpleName() + "[name=" + name + "]";
}
Which would print, e.g., Person[name=Henry]. That's a really useful piece of data for debugging/testing.
If you want to focus on just one aspect of your object or include a lot of jazzy formatting, you might be better to define a separate method instead, e.g. String toElegantReport() {...}.
Auto-generating the Output
Many IDEs offer support for auto-generating a toString() method, based on the fields in the class. See docs for Eclipse and IntelliJ, for example.
Several popular Java libraries offer this feature as well. Some examples include:
ToStringBuilder from Apache Commons Lang
MoreObjects.ToStringHelper from Google Guava
#ToString annotation from Project Lombok
Printing groups of objects
So you've created a nice toString() for your class. What happens if that class is placed into an array or a collection?
Arrays
If you have an array of objects, you can call Arrays.toString() to produce a simple representation of the contents of the array. For instance, consider this array of Person objects:
Person[] people = { new Person("Fred"), new Person("Mike") };
System.out.println(Arrays.toString(people));
// Prints: [Fred, Mike]
Note: this is a call to a static method called toString() in the Arrays class, which is different to what we've been discussing above.
If you have a multi-dimensional array, you can use Arrays.deepToString() to achieve the same sort of output.
Collections
Most collections will produce a pretty output based on calling .toString() on every element.
List<Person> people = new ArrayList<>();
people.add(new Person("Alice"));
people.add(new Person("Bob"));
System.out.println(people);
// Prints [Alice, Bob]
So you just need to ensure your list elements define a nice toString() as discussed above.

I think apache provides a better util class which provides a function to get the string
ReflectionToStringBuilder.toString(object)

Every class in Java has the toString() method in it by default, which is called if you pass some object of that class to System.out.println(). By default, this call returns the className#hashcode of that object.
{
SomeClass sc = new SomeClass();
// Class # followed by hashcode of object in Hexadecimal
System.out.println(sc);
}
You can override the toString method of a class to get different output. See this example
class A {
String s = "I am just a object";
#Override
public String toString()
{
return s;
}
}
class B {
public static void main(String args[])
{
A obj = new A();
System.out.println(obj);
}
}

In Eclipse,
Go to your class,
Right click->source->Generate toString();
It will override the toString() method and will print the object of that class.

I prefer to use a utility function which uses GSON to de-serialize the Java object into JSON string.
/**
* This class provides basic/common functionalities to be applied on Java Objects.
*/
public final class ObjectUtils {
private static final Gson GSON = new GsonBuilder().setPrettyPrinting().create();
private ObjectUtils() {
throw new UnsupportedOperationException("Instantiation of this class is not permitted in case you are using reflection.");
}
/**
* This method is responsible for de-serializing the Java Object into Json String.
*
* #param object Object to be de-serialized.
* #return String
*/
public static String deserializeObjectToString(final Object object) {
return GSON.toJson(object);
}
}

In intellij you can auto generate toString method by pressing alt+inset and then selecting toString() here is an out put for a test class:
public class test {
int a;
char b;
String c;
Test2 test2;
#Override
public String toString() {
return "test{" +
"a=" + a +
", b=" + b +
", c='" + c + '\'' +
", test2=" + test2 +
'}';
}
}
As you can see, it generates a String by concatenating, several attributes of the class, for primitives it will print their values and for reference types it will use their class type (in this case to string method of Test2).

By default, every Object in Java has the toString() method which outputs the ObjectType#HashCode.
If you want more meaningfull information then you need to override the toString() method in your class.
public class Person {
private String name;
// constructor and getter/setter omitted
// overridding toString() to print name
public String toString(){
return name;
}
}
Now when you print the person object using System.out.prtinln(personObj); it will print the name of the person instead of the classname and hashcode.
In your second case when you are trying to print the array, it prints [Lcom.foo.Person;#28a418fc the Array type and it's hashcode.
If you want to print the person names, there are many ways.
You could write your own function that iterates each person and prints
void printPersonArray(Person[] persons){
for(Person person: persons){
System.out.println(person);
}
}
You could print it using Arrays.toString(). This seems the simplest to me.
System.out.println(Arrays.toString(persons));
System.out.println(Arrays.deepToString(persons)); // for nested arrays
You could print it the java 8 way (using streams and method reference).
Arrays.stream(persons).forEach(System.out::println);
There might be other ways as well. Hope this helps. :)

If you Directly print any object of Person It will the ClassName#HashCode to the Code.
in your case com.foo.Person#2f92e0f4 is getting printed . Where Person is a class to which object belongs and 2f92e0f4 is hashCode of the Object.
public class Person {
private String name;
public Person(String name){
this.name = name;
}
// getter/setter omitted
#override
public String toString(){
return name;
}
}
Now if you try to Use the object of Person then it will print the name
Class Test
{
public static void main(String... args){
Person obj = new Person("YourName");
System.out.println(obj.toString());
}
}

If you look at the Object class (Parent class of all classes in Java) the toString() method implementation is
public String toString() {
return getClass().getName() + "#" + Integer.toHexString(hashCode());
}
whenever you print any object in Java then toString() will be call. Now it's up to you if you override toString() then your method will call other Object class method call.

Using Lombok #Data annotation on class will provide getter, setter, toString and hashcode. Using Lombok is better as it handles boilerplate code.

For a "deep" toString() there is an alternative to the JSON based answers (Jackson, GSON, etc.): ReflectionToStringBuilder from the Apache Commons Lang 3 library, with RecursiveToStringStyle or MultilineRecursiveToStringStyle. Code example:
System.out.println("My object: " +
ReflectionToStringBuilder.toString(theObject, new RecursiveToStringStyle()));
Output examples:
// RecursiveToStringStyle
Person#7f54[name=Stephen,age=29,smoker=false,job=Job#43cd2[title=Manager]]
// MultilineRecursiveToStringStyle
Person#7f54[
name=Stephen,
age=29,
smoker=false,
job=Job#43cd2[
title=Manager
]
]

I managed to get this done using Jackson in Spring 5. Depending on the object it might not work in all cases.
import com.fasterxml.jackson.databind.ObjectMapper;
ObjectMapper mapper = new ObjectMapper();
System.out.println(mapper.writeValueAsString(yourObject));
the output would look like
{
"id" : 1,
"fieldOne" : "string"
}
Here are more examples using Jackson
If you use GSON instead It might look like
Gson gson = new Gson();
System.out.println(gson.toJson(yourObject));

If you are using project Lombok you could use the #ToString annotation and generate a standard toString() method without adding boilerplate.
import lombok.ToString;
#ToString
public class LoginDto {
private String user;
private String pass;
}
...
System.out.println(loginDto.toString());
// LoginDto(user=x#xxx.x, pass=xxxxx)

Related

Camel set body to object with header expression

Is it possible to set a response body to an object and pass in a camel header property. I can achieve this in a processor but I'd rather do it in line of the route.
.setBody(constant(
new Foo()
.withOne("HelloWorld")
.withTwo(simple("Header property is ${header.uniqueProperty}").toString())
))
With the above code I get a response of:
<foo>
<one>HelloWorld</one>
<two>Header property is ${header.uniqueProperty}</two>
</foo>
Here is my POJO
#XmlRootElement
#XmlAccessorType(XmlAccessType.FIELD)
public class Foo {
private String one;
private String two;
public String getOne() {
return one;
}
public void setOne(final String one) {
this.one = one;
}
public String getTwo() {
return two;
}
public void setTwo(final String two) {
this.two = two;
}
public Foo withOne(final String one) {
setOne(one);
return this;
}
public Foo withTwo(final String two) {
setTwo(two);
return this;
}
}
constant() probably won't work for you, since you probably want this dynamically evaluated for every exchange that passes through. Since you need to set the body to a newly instantiated object, you need a mechanism that's capable of this. You mentioned you want to avoid a processor, but I'd like to point out how simple this could be done in the route:
.setBody(exchange -> new Foo()
.withOne("HelloWorld")
.withTwo(simple("Header property is " + exchange.getIn().getHeader("uniqueProperty")))
)
Edit: Actually this is not a processor. We're just passing a lambda (Function) to setBody().
If you're in a Spring environment, you could use spring expression language:
.setBody().spel("#{new Foo()" +
".withOne('HelloWorld')" +
".withTwo(simple('Header property is ' + request.headers.uniqueProperty))}");

How to find a specific field from a genetic List object in wpf

I am trying to create a generic class for finding duplicate values for different class.
I am casting each list to an object and passing it as parameter like this
List<StudentModel1> a = new List<StudentModel1>();
List<StudentModel2> b = new List<StudentModel2>();
List<StudentModel3> c = new List<StudentModel3>();
List<object> obj = a.Cast<object>().ToList();//like this
public bool Duplicate(List<object> obj, string Fieldname, string Name)
{
if (obj.Any(x => x.Fieldname.Contains(Name))) { return true; } else { return false; }
}/// something like this;
here i am passing fieldname propery ,string name and object for finding duplicate and return a bool.How to access field name in linq.
please help how to acheive this.
thanks.
If I understand your question correctly, you have 3 different versions of a class: StudentModel1, StudentModel2 and StudentModel3 and you want to be able to compare lists of them. You are casting them to Object so that you can pass any any version of that class to your Duplicate method.
Assuming the above is correct, what you need is inheritance. If that's not something your familiar with you should definitely read up on it.
Consider the following:
class StudentModelBase
{
public string SomeProperty { get; set; }
}
class StudentModel1 : StudentModelBase
{
}
class StudentModel2 : StudentModelBase
{
}
class StudentModel3 : StudentModelBase
{
}
If your Duplicate method should be able to handle any of the "StudentModel" classes, then that means the information needed to tell if there are duplicates must be common to all three versions of that class. The properties and fields which store that information should be moved into StudentModelBase. Then, instead of casting to Object you should cast to StudentModelBase.
Your cast becomes:
List<StudentModelBase> base = a.Cast<StudentModelBase>().ToList();
And your Duplicate method becomes something like the following:
public bool Duplicate(List<StudentModelBase> obj, string Name)
Notice I left out Fieldname because if this is implemented correctly you shouldn't need to pass that as a parameter. You should just be able to access the need members of StudentModelBase like any normal variable, since they should be the same for all versions of "StudentModel".

(Unity) Why is my list of a class not getting saved in JSON

I want to save a list of dialogue items. I made a script called dialogue item which is just one message, I made an array of that so it can be a conversation, and I made a list of that conversation so that I can have multiple conversations.
[SerializeField] public List<DialogueList> dialogue = new List<DialogueList();
So I made this variable of a class named DialogueList, that contains the dialogueitems.
[System.Serializable]
public class DialogueList
{
[SerializeField] public string convoName;
[SerializeField] public int dialogueID;
[SerializeField] public DialogueItem[] dialogues;
}
I want to save these conversations so that I can load them in specific languages in later stages. But for some reason my JSON file is empty when I try to save my variable named dialogue.
string jsonData = JsonUtility.ToJson(dialogue, true);
string _fullPath = "/caroline-dialogue" + ".json";
File.WriteAllText(Application.persistentDataPath + _fullPath, jsonData);
I tried using a different method, that actually works, but it can get really messy.
for (int i = 0; i < dialogue.Count; i++)
{
string jsonData = JsonUtility.ToJson(dialogue[i], true);
string _fullPath = "/caroline-dialogue-" + i + ".json";
File.WriteAllText(Application.persistentDataPath + _fullPath, jsonData);
}
My question is: What am I doing wrong? Am I forgetting something? My guess it that something is wrong with the variable named dialogue, since saving all the dialogueitems with a for loop works.
I hope I explained my problem well enough.
Serialization/deserialization of the arrays or lists is not supported using the JsonUtility. You would need to wrap the list in a serializable class:
[Serializable]
private class DialogueListWrapper
{
public List<DialogueList> objects;
}

How to deserialize several nested Json arrays (more than 2) using DataContractJsonSerializer (Windows Phone 7)

I need to deserialize the next Json string that has several nested Json arrays:
{"d1":[["11791452",[["980",""]]],["11791453",[["1060",""],["1140",""],["1220",""],["1300",""]]],["11791454",[["1070",""]]]]}
I try to do it in several steps, so far I'm able to deserialize three levels of nested arrays. As follow:
{"aOaOa":[[["1060",""],["1140",""],["1220",""],["1300",""]]]}
public class ThreeSimpleNestedArrays
{
public List<List<string[]>> aOaOa; //array of arrays of arrays
public ThreeSimpleNestedArrays()
{
aOaOa = new List<List<string[]>>();
}
}
But the problem arise when I add the extra string in the array structure:
{"TEST": [["11791453",[["1060",""],["1140",""],["1220",""],["1300",""]]],["123456",[["0","1"],["2","3"]]]]}
public class ComplexNestedArray
{
public List<Dictionary<string,List<string[]> >> TEST;
public ComplexNestedArray()
{
TEST = new List<Dictionary<string, List<string[]>>>();
}
}
I'm getting the next error message:
"Unable to cast object of type 'System.String' to type 'System.Collections.Generic.Dictionary`2[System.String,System.Object]'."
What am I missing?
Can anybody suggest a way to deserialize an object like this nested within Json arrays using DataContractJsonSerializer?
The code I use to deserialize is the next:
//Works
DataContractJsonSerializer dcJsonSer = new DataContractJsonSerializer(typeof(ThreeSimpleNestedArrays));
ThreeSimpleNestedArrays root = (ThreeSimpleNestedArrays)dcJsonSer.ReadObject(str);
//Don't work
DataContractJsonSerializer dcJsonSer = new DataContractJsonSerializer(typeof(ComplexNestedArray));
ComplexNestedArray root = (ComplexNestedArray)dcJsonSer.ReadObject(str);
Btw, I'm able to deserilize the object when it is serilized as a Json Object as follow:
{"TEST": [{"s": "11791453","aOa": [["1060",""],["1140",""],["1220",""],["1300",""]]},{"s": "123456","aOa":[["0","1"],["2","3"]]}]}
using a class with two members (a string "s" and a List of string[] "aOa"), but without the names, when the object is serialized as an array, I'm unable to do it.
Any suggestion?
Ok, it looks like the DataContractJsonSerializer is smarter than I though .
It turns out that the way to deserialize that kid of nested objects array is with a class like this:
public class ComplexNestedArray
{
//{"TEST": [["11791453",[["1060",""],["1140",""],["1220",""],["1300",""]]],["123456",[["0","1"],["2","3"]]]]}
public List<List<object>> TEST { get; set; }
}
After that, it is only a mater to do a couple of for cycles and casts to the appropriate class structure.
Btw, This is a MUST in your toolbox in case you have to deal with Json:
json2csharp
Here is my solution. However I'll try to add later a way for your full json:
class Program {
static void Main(string[] args) {
new Program();
}
public Program() {
string full = "{\"d1\":[[\"11791452\",[[\"980\",\"\"]]],[\"11791453\",[[\"1060\",\"\"],[\"1140\",\"\"],[\"1220\",\"\"],[\"1300\",\"\"]]],[\"11791454\",[[\"1070\",\"\"]]]]}";
string simple1 = "{\"aOa\":[[\"1060\",\"\"],[\"1140\",\"\"],[\"1220\",\"\"],[\"1300\",\"\"]]}";
string simple2 = "{\"aOaOa\":[[[\"1060\",\"\"],[\"1140\",\"\"],[\"1220\",\"\"],[\"1300\",\"\"]]]}";
DataContractJsonSerializer d1 = new DataContractJsonSerializer(typeof(S1));
S1 r1 = (S1)d1.ReadObject(new MemoryStream(Encoding.Default.GetBytes(simple1)));
DataContractJsonSerializer d2 = new DataContractJsonSerializer(typeof(S2));
S2 r2 = (S2)d2.ReadObject(new MemoryStream(Encoding.Default.GetBytes(simple2)));
Console.WriteLine("done");
Console.ReadKey();
}
[DataContract]
class S1 {
[DataMember]
List<List<String>> aOa;
}
[DataContract]
class S2 {
[DataMember]
List<List<List<string>>> aOaOa;
}
}

Collection is empty when returning from JAX-RS/CXF service

I have a service method defined as:
public JaxbList<Deal> getDeal() {
List<Deal> deals = new ArrayList<Deal>();
Deal type = new Deal();
type.setDealID(1);
type.setName("June Discounts");
deals.add(type);
JaxbList list = new JaxbList(deals);
System.out.println("List size -> " + list.getList().size());
return list;
}
My client is defined as:
WebClient client = WebClient.create("....");
JaxbList deals = client.path("exampleservice/getDeal")
.accept("application/xml").get(JaxbList.class);
List<Deal> types = deals.getList();
When I print out the size of the collection in the service method, the result comes back as 1. But, the size of my 'types' list from the client is 0. When I open in a browser, the 1 deal is displayed. So, this issue seems to be my client. I'm not sure where though.
Ideas?
Here is my JaxbList class:
public class JaxbList<T>{
protected List<T> list;
public JaxbList(){}
public JaxbList(List<T> list){
System.out.println("Setting list...");
this.list=list;
}
#XmlElement(name="Item")
public List<T> getList(){
return list;
}
}
As mentioned above by KasunBG your public JaxbList(List<T> list) constructor is never called by JAXB. The default no-arg one is used instead (see some discussion at What JAXB needs a public no-arg constructor for?). Actually Java compiler should complain about this situation with two constructors and "never initialized field list".
The solution is to introduce a setList() setter and throw a runtime exception from a no-arg constructor.

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