Thread: Collections.sort

Here's another look at code tags:

[code=java]
<YOUR CODE HERE>
[/code]

This compiles and runs well:

public class IntegerTest implements Comparator<Integer>{
@Override
public int compare(Integer o1, Integer o2){
return (o1<o2 ? -1 : (o1==o2 ? 0 : 1));
}
 
 
/**
* @param args the command line arguments
*/
public static void main(String[] args) {
List<Integer> arrayList = new ArrayList<>();
arrayList.add(12);
arrayList.add(5);
arrayList.add(7);
arrayList.add(4);
arrayList.add(5);
arrayList.add(16);
arrayList.add(13);
arrayList.add(2);
System.out.println(arrayList);
Collections.sort (arrayList, new IntegerTest());
for (Integer integer : arrayList){
System.out.println (integer);
 
}
}
}

The code below gives me an error at 28:
non-static variable this cannot be referenced from a static context

no suitable method found for sort(Collection<Integer>,gtleHw4.ListSorter)
method Collections.<T#1>sort(List<T#1>,Comparator<? super T#1>) is not applicable
(no instance(s) of type variable(s) T#1 exist so that argument type Collection<Integer> conforms to formal parameter type List<T#1>)
method Collections.<T#2>sort(List<T#2>) is not applicable
(cannot instantiate from arguments because actual and formal argument lists differ in length)
where T#1,T#2 are type-variables:
T#1 extends Object declared in method <T#1>sort(List<T#1>,Comparator<? super T#1>)
T#2 extends Comparable<? super T#2> declared in method <T#2>sort(List<T#2>
The only difference I see is the while lop reading integers from a file.

1.	    
2.	   public class ListSorter implements Comparator<Integer>{
3.	       
4.	       @Override
5.	       public int compare(Integer o1, Integer o2){
6.	           return (o1>o2 ? -1 : (o1==o2 ? 0 : 1));
7.	       }
8.	       
9.	   }
10.	    public static void main(String[] args)throws IOException {
11.	        java.io.File intDat = new java.io.File("intDat");
12.	        try (java.io.PrintWriter create = new java.io.PrintWriter (intDat)) {
13.	            create.print("23 45 67 12 9 44 14 21 78 95 6 89 7 42 28 34");
14.	        }
15.	        Collection<Integer> intList;        
16.	        try (Scanner read = new Scanner (intDat)) {
17.	            intList = new ArrayList<>();
18.	            //List<Integer> arrayList = new ArrayList<>();
19.	            while (read.hasNext()){
20.	                intList.add(read .nextInt());
21.	                
22.	                   
23.	             System.out.println(intList);
24.	            }
25.	        }
26.	        //System.out.println(arrayList);
27.	           
28.	          Collections.sort (intList, new ListSorter());
29.	            for (Integer integer : intList){
30.	                System.out.println (integer);
31.	            }
32.	            
33.	                   }
34.	    }
35.	
36.

Where are the line numbers showing where in the source file the errors happened?

non-static variable this cannot be referenced from a static context

error at 28

Where is the "this" variable on line 28?

Use the javac command to get good error messages.
Here is a sample:

TestSorts.java:138: cannot find symbol
symbol  : variable var
location: class TestSorts
         var = 2;
         ^