So, can I use same name for public variable in a class and method argument in java? for example("number" is declared twice):

public class Class1 {
    public int number;

    public static String function1(String id,int number)
    {
        //do something

    }
}

Yes you can.

The int number declared in the method is only accesible inside de method.

The int number declared as property in the class is accesible in any method for the class.

If you want to access to the number property inside the method, you must use this.

Example:

public static String function1(String id,int number)
{
    this.number = number;
}