Create instance of a class and set variables

Question

in C# you can create a instance of a class and set the values of variables at the same time:

public class Object
{
    public virtual long Id { get; set; }
    public string Name { get; set; }
    public string Description { get; set; }
    public int Version { get; set; }
    public long ParentId { get; set; }
}

public class Start
{ 
     Object object= new Object()
     {
         Id = 1,
         Name = name,
         ParentId = parentId,
         Description = null,
         Version= 2
     };
}

Is this possible in Java aswell and how?

explv · Accepted Answer · 2016-07-04 10:22:17Z

The standard way for setting values when creating an instance is to just have a constructor:

class ExampleObject {
    long id;
    String name;
    String description;
    int version;
    long parentId;

    public ExampleObject(final long id, final String name, final String description, final int version, final long parentId) {
        this.id = id;
        this.name = name;
        this.description = description;
        this.version = version;
        this.parentId = parentId;
    }
}

And then call it like:

ExampleObject exampleObject = new ExampleObject(1, name, null, 2, parentId);

It is possible to use a similar syntax to what you have shown, but it has quite a few downsides which you should research about before using it (and you also cannot use variables with this):

ExampleObject exampleObject = new ExampleObject() {{
    id = 1;
    name = "";
    parentId = 2;
    description = null;
    version = 2;
}};


class ExampleObject {
    long id;
    String name;
    String description;
    int version;
    long parentId;
}

What this does is creates an anonymous class with a static initialiser block. A static initialiser block looks like:

class ExampleObject {
    long id;
    String name;
    String description;
    int version;
    long parentId;

    {
        id = 1;
        name = "";
        parentId = 2;
        description = null;
        version = 2;
    }
}

carcaret · Accepted Answer · 2016-07-04 10:23:59Z

You can create a constructor that accepts values for all the fields. This way, you can create a new instance of that object and set the values you want at the same time:

public class MyClass {
  public long id;
  public String name;
  public String description;
  public int version;
  public long parentId;

  /** Constructor **/
  public MyClass(long id, String name, String description, int version, long parentId) {
    this.id = id;
    this.name = name;
    this.description = description;
    this.version = version;
    this.parentId = parentId;
  }
}

public static void main(String args[]) {
  MyClass myClass = new MyClass(1, "name", "description", 1, 1);
}

By the way, it's not recommended (although you can) to name a class Object in Java, since Java also has a class with that very same name, and all Java classes extend from it (can lead to confussion).

Mowgli · Accepted Answer · 2016-07-05 04:54:37Z

0

              public class Object
              {
                public long id;
                 public String name;
               public String description;
                public int version;
              public long parentId;

                  public Object(long Id,string Name,string Description,int                Version,long Parent_Id)
                {

                 this.Id =Id ;
                 this.Name =Name ;
                  this.Description =Description ;
                 this.Version =Version ;
                 }

answered Jul 5, 2016 at 4:54

Mowgli

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