Question

I am brand new to Java 🙂

I have 2 String lists and I was wondering what would be the most efficient way to compare the two and have a resulting array which contains strings that are not in the other. For example, I have a list called oldStrings and one called Strings. I have seen the Comparator function but don’t fully understand how it works, right now I was thinking I could create a for loop, loop through each string and then save that string:

for (final String str : oldStrings) {
  if(!strings.contains(str))
  {                     
    getLogger().info(str + " is not in strings list ");
  }
}

There’s going to be up to 200 strings in this list. Would this be the best way to go about this? Thank you!

Answer 1

Collection firstList = new ArrayList() {{
    add("str1");
    add("str2");
}};

Collection secondList = new ArrayList() {{
    add("str1");
    add("str3");
    add("str4");
}};


System.out.println("First List: " + firstList);
System.out.println("Second List: " + secondList);

// Here is main part
secondList.removeAll(firstList);

System.out.println("Result: " + secondList);  

Update:
More sophisticated version of code

Collection<String> firstList = new ArrayList<String>();
firstList.add("str1");
firstList.add("str2");

Collection<String> secondList = new ArrayList<String>();
secondList.add("str1");
secondList.add("str2");
secondList.add("str3");


System.out.println("First List: " + firstList);
System.out.println("Second List: " + secondList);

// Here is main part
secondList.removeAll(firstList);  

Update:

To Get acctual difference between both String list go for this.

    Set<String> setOne = new HashSet<String>();        
    Set<String> setTwo = new HashSet<String>();
    setOne.add("1");
    setOne.add("2");
    setOne.add("5");
    setTwo.add("1");
    setTwo.add("3");
    setTwo.add("4");
    Set<String> setTwoDummy = new HashSet<String>(setTwo);
    setTwo.retainAll(setOne);        
    setTwoDummy.addAll(setOne);
    setTwoDummy.removeAll(setTwo);
    System.out.println(""+setTwoDummy);