CODEWITHSUNDEEP
javalistloops
DjShon
DjShon

Reputation: 263

How to check whether a List<String> contains a specific string?

Here's what I'm trying to do: I have some List<String>, I want to print a statement if the List contains a particular string, else throw an Exception but when I try the following code

List<String> fruit = new ArrayList<>();
fruit.add("apple");
fruit.add("orange");
fruit.add("banana");

for(int i = 0; i < fruit.size(); i++){
   if(fruit.get(i).contains("banana"){
     System.out.println("Found");
   } else {
     throw new SkipException("could not be found");
   }
}

it iterates through the List and at i = 0 it obviously finds "apple" and immediately goes to the else block and throws exception. I also tried the following, but this didn't work either. 

for(int i = 0; i < fruit.size(); i++){
   if(Arrays.asList(fruit).contains("banana"){
      System.out.println("found");
   }else{
      throw new SkipException("not found");
   }
}

Is there an easy way to do what I'm trying to do here?

Upvotes: 17

Views: 90951

Answers (4)

Syed Haris Ali Ghaznavi
Syed Haris Ali Ghaznavi

Reputation: 787

try using this if at any index the value is equal to "banana" and it will print found else it will throw exception

   List<String> fruit = new ArrayList<>();
   fruit.add("apple");
   fruit.add("orange");
   fruit.add("banana");

   boolean result;
   for(int i = 0; i < fruit.size(); i++){
      result = fruit.get(i).equals("banana");
      if(result){
        break; // Early exit if found
      }
   }

   if(result){
      System.out.println("Found");
   } else {
      throw new SkipException("could not be found");
   }

Solution 2: when working with arraylists you dont need to iterate through every index manually rather arraylist gives you a function "contains()" that will automatically check if the desired value is present at any index or not so simply you can do this:

    if(fruit.contains("banana"){
         System.out.println("Found");
    } else {
         throw new SkipException("could not be found");
     }

Upvotes: 0

Craig Otis
Craig Otis

Reputation: 32104

There are a few ways.

Which one you choose is up to you, there's a tradeoff between verbosity, being constrained to a simple equals check (if you want to do more complicated matching, you can't easily do Option 1), and using newer APIs that you might not yet support or be familiar with.

Option 1: The Collection.contains() method:

List<String> fruits = new ArrayList<>();
fruits.add("apple");
fruits.add("orange");
fruits.add("banana");

if (fruits.contains("banana") {
    System.out.println("Found");
} else {
    throw new SkipException("could not be found");
}

Option 2: Using a for loop with external state:

List<String> fruits = new ArrayList<>();
fruits.add("apple");
fruits.add("orange");
fruits.add("banana");

boolean found = false;
for (String s : fruits) {
    if (s.equals("banana")) {
        found = true;
        break; // Break out of the loop to skip the remaining items
    }
}
if (found) {
    System.out.println("Found");
} else {
    throw new SkipException("could not be found");
}

Option 3: If you're using Java 8, the neat Stream.anyMatch() method:

List<String> fruits = new ArrayList<>();
fruits.add("apple");
fruits.add("orange");
fruits.add("banana");

if (fruits.stream().anyMatch(s -> s.equals("banana"))) {
    System.out.println("Found");
} else {
    throw new SkipException("could not be found");
}

Option 3 is my personal favorite, as it's nearly as compact as Option 1, but allows to to provide a more complex Predicate if you want a comparison based on something other than the equals() method.

Upvotes: 31

MidasLefko
MidasLefko

Reputation: 4559

Try using a boolean to detect whether you have found the fruit in your list of fruits. Something like this:

boolean inlist = false;

for(int i = 0; i < fruit.size(); i++){
   if(fruit.get(i).equals("banana"){
        inlist = true
        break;
   }
}

if (inlist) {
    System.out.println("found");
} else {
    throw new SkipException("not found");
}

Upvotes: -1

Imesha Sudasingha
Imesha Sudasingha

Reputation: 3570

You don't have to iterate through the array list. Once you call list.contains("someString"), it will check for that string in that entire array list. Therefore, the following is enough.

if(fruit.contains("banana"){
     System.out.println("Found");
} else {
     throw new SkipException("could not be found");
}

Upvotes: 2

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