Java constructor method with optional parameters

Question

Possible Duplicate    Java optional parameters       I know that in PHP if you want to call a function with less parameters you declare the function like   function foo int param1  int param2    2      and now I can call foo 2  and param2 will be set to 2   I tried to do this in a Java constructor but it seems it isn t possible  Is there a way to do this or i just have to declare two constructors   Thanks

User · Answer

You can simulate it with using varargs  however then you should check it for too many arguments   public void foo int param1  int     param2       int param2     if param2 length    0        param2    2    else if para2 length    1        param2    param2 0     else       throw new TooManyArgumentsException       user provided too many arguments         rest of the code     However this approach is not a good way of doing this  therefore it is better to use overloading

User · Answer

Why do you want to do that   However  You can do this   public void foo int param1        int param2   2         rest of code     or   public void foo int param1  int param2           rest of code    public void foo int param1        foo param1  2

User · Answer

You can t have optional arguments that default to a certain value in Java  The nearest thing to what you are talking about is java varargs whereby you can pass an arbitrary number of arguments  of the same type  to a method

User · Answer

Java doesn t have the concept of optional parameters with default values either in constructors or in methods  You re basically stuck with overloading  However  you chain constructors easily so you don t need to repeat the code   public Foo int param1  int param2        this param1   param1      this param2   param2     public Foo int param1        this param1  2

User · Answer

You can use varargs for optional parameters   public class Booyah       public static void main String   args            woohoo 1           woohoo 2  3             static void woohoo int required  Integer    optional            Integer lala          if  optional length    1                lala   optional 0             else               lala   2                    System out println required   lala             Also it s important to note the use of Integer over int  Integer is a wrapper around the primitive int  which allows one to make comparisons with null as necessary

User · Answer

Java doesn t support default parameters  You will need to have two constructors to do what you want   An alternative if there are lots of possible values with defaults is to use the Builder pattern  whereby you use a helper object with setters   e g      public class Foo        private final String param1       private final String param2        private Foo Builder builder           this param1   builder param1         this param2   builder param2              public static class Builder          private String param1    defaultForParam1          private String param2    defaultForParam2           public Builder param1 String param1             this param1   param1           return this                  public Builder param2 String param1             this param2   param2           return this                  public Foo build              return new Foo this                          which allows you to say   Foo myFoo   new Foo Builder   param1  myvalue   build      which will have a default value for param2

[java] Java constructor/method with optional parameters?

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