Question

Ruby has conditional initialization. Apparently, Java does not or does it? I try to write more succintly, to limit the range as small as possible.

import java.io.*;
import java.util.*;

public class InitFor{

        public static void main(String[] args){
                for(int i=7,k=999;i+((String h="hello").size())<10;i++){}

                System.out.println("It should be: hello = "+h);

        }
}

Errors

Press ENTER or type command to continue
InitFor.java:8: ')' expected
  for(int i=7,k=999;i+((String h="hello").size())<10;i++){}
                              ^

Puzzles

1. Is it possible to assign a value to an declared value in while-loop? YES code1
2. Assignment in for-loop conditional? YES code2
3. conditional init NO
4. Can you assign different types of values in loops? YES in a reply
5. Some rule for initialization inside loops? Declare outside to access values later, what about init? (?)

1. CODE

import java.io.*;
import java.util.*;

public class InitFor{
        public static void main(String[] args){
                int k=5;
                while((k=(k%3)+1)!=1){
                        System.out.println(k);
                }
                //PRINTs only 3
        }
}

2. CODE

import java.io.*;
import java.util.*;

public class InitFor{

        public static void main(String[] args){
                int k=5;
                for(;(k=(k%3)+1)!=1;){
                        System.out.println(k);
                }
                //PRINTs only 3
                System.out.println(k); 
                // WHY DOES IT PRINT 1? Assign in for-loop!
        }
}

Part of the Original problem with many different kind of assignments and initializations — 100lines of code in one-liner

for(int t=0,size=(File[] fs=((File f=f.getParentFile()).listFiles(filt))).size();fs==null;t++){if(t>maxDepth){throw new Exception("No dir to read");}}

Answer 1

I think you are confusing assignment with declaration. You could do

public static void main(String[] args){
    String h = null;
    for(int i=7,k=999;i+((h="hello").size())<10;i++){}

    System.out.println("It should be: hello = "+h);
}

the =’s operator is right associative and sets the first argument to the second argument and evaluates to the first argument, so something like

a = b = c = 4

is the same as

(a = (b = (c = 4)))

which sets c to 4, b to c (now 4) and a to b (now also 4)

your one line of code could be (reformatted for clarity)

File[] fs=null;                                                                            
File f= ??? ; //you never initialize f in the for loop, you need a starting value  
int t, size;                                                                               

for (t=0,size=(fs=((f=f.getParentFile()).listFiles(filt))).size();      
     fs==null;                                                                             
     t++) {
       if(t>maxDepth) {throw new Exception("No dir to read");}
     }
}

EDIT – (though that’s really ugly code and if you checked it in on my project I’d be telling you to rewrite it ASAP)