Here is an example  using the Comparable interface.
Let say, you have MyObject which consists of 'key' and 'value',
and you want to sort it by the 'value';

=====================================================
import java.util.*;

public class  Test {
public Test(String[] args) throws  Exception {
MyObject[] o = {new MyObject("ADF", "SKAK"),
new MyObject("S", "DJD"),
new MyObject("ADF", "DJD"),
new MyObject("XDJD", "ZSKSK"),
new MyObject("ZDS", "XSSS")};
List l = Arrays.asList(o);
System.out.println(l + "\n");
Collections.sort(l);
System.out.println(l);
}

public static  void main(String[] args) {
try {
new Test(args);
} catch (Exception e) {
e.printStackTrace();
}
}

private class MyObject implements Comparable {
private String key;
private String value;

public MyObject(String key, String value) {
this.key = key;
this.value = value;
}

public boolean equals(Object o) {
if (o instanceof MyObject) {
MyObject mo = (MyObject) o;
return this.key.equals(mo.key) && this.value.equals(mo.value);
} else {
return false;
}
}

public String toString() {
return key + " " + value;
}

public int  compareTo(Object o) {
MyObject mo = (MyObject) o;
int x = value.compareTo(mo.value);
// if value is equal, then sort the key
return (x != 0) ? x : key.compareTo(mo.key);
}
}
}

I hope this is what you are looking for.