Question

Say I have the following:

Class myclass
{
    public string stra ="", strb = ""
    myclass(String a, String b){stra=a;strb=b}
}


//then in the app I want to do:

myclass myclassinst1 = new myclass("blah","xxxx");
myclass myclassinst2 = new myclass("blah2","yyyy");
myclass myclassinst3 = new myclass("blah3","zzzz");

list <myclass> mylist = new ArrayList<myclass>();
mylist.add(myclassinst1 );
mylist.add(myclassinst2 );
mylist.add(myclassinst3 );

//How would I then convert that to a String[] Array of all the stra elements without using a loop.
//eg: 
String[] strarr_a = mylist.toarray(myclass.stra);
String[] strarr_b = mylist.toarray(myclass.strb);


//instead of having to do
String[] strarr_a = new String[mylist.size()];
String[] strarr_b = new String[mylist.size()];
for (int i=0;i<mylist.size();i++)
{
   strarr_a[i] = mylist.get(i).stra;
   strarr_b[i] = mylist.get(i).strb;
}

Answer 1

There is no easy way to do this, for example with a standard Java API method. You will have to write the loop yourself.

Note that there are a number of errors in your code (missing semi-colons, misspelled class names such as string and list, and the keyword is class, not Class).

I’d write it something like this:

class MyClass {
    // Note that it's bad practice to make fields public.
    // Also, you do not need to initialize fields to "" if you're going to initialize them in the constructor.
    private String stra;
    private String strb;

    public MyClass(String a, String b) {
        this.stra = a;
        this.strb = b;
    }

    public String getStra() {
        return stra;
    }

    public String getStrb() {
        return strb;
    }
}

MyClass myclassinst1 = new MyClass("blah","xxxx");
MyClass myclassinst2 = new MyClass("blah2","yyyy");
MyClass myclassinst3 = new MyClass("blah3","zzzz");

List<MyClass> mylist = new ArrayList<MyClass>();
mylist.add(myclassinst1);
mylist.add(myclassinst2);
mylist.add(myclassinst3);

List<String> list1 = new ArrayList<String>();
List<String> list2 = new ArrayList<String>();

for (MyClass obj : mylist) {
    list1.add(obj.getStra());
    list2.add(obj.getStrb());
}

String[] strarrA = list1.toArray(new String[list1.size()]);
String[] strarrB = list2.toArray(new String[list2.size()]);