CODEWITHSUNDEEP
javaarraysregexsubstringindexof
Ravichandra
Ravichandra

Reputation: 2352

Index of a element in array using substring

I need to get the index of an element in array to be searched:

 String[] items = {"One:10.1.22.33", "Two:10.1.21.23", "Three:10.1.21.33", "Four:10.1.21.23", "Five:10.1.22.23"};
 String q = "Two";  //need to find index of element starting with sub-sting "Two"

what I tried

Try-1

    String temp = "^"+q;    
    System.out.println(Arrays.asList(items).indexOf(temp));

Try-2

items[i].matches(temp)
for(int i=0;i<items.length;i++) {
    if(items[i].matches(temp)) System.out.println(i);
}

Both are not working as expected.

Upvotes: 4

Views: 1678

Answers (3)

Santhosh Kumar
Santhosh Kumar

Reputation: 1

String q= "Five";String pattern = q+"(.*)";
for(int i=0;i<items.length;i++)
{
if(items[i].matches(pattern))
 { 
  System.out.println(i);
 }
}

Upvotes: -1

Yodism
Yodism

Reputation: 247

I think you will need to implement LinearSearch for this but with a twist, you were searching for substring. You can try this.

String[] items = {"One:10.1.22.33", "Two:10.1.21.23", "Three:10.1.21.33", "Four:10.1.21.23", "Five:10.1.22.23"};
String q= "Two";  //need to find index of element starting with sub-sting "Two"

for (int i = 0; 0 < items.length; i++) {
    if (items[i].startsWith(q)){
        // item found
        break;
    } else if (i == items.length) {
        // item not found
    }
}

Upvotes: 0

Tunaki
Tunaki

Reputation: 137319

You would be better off using startsWith(String prefix) like this:

String[] items = {"One:10.1.22.33", "Two:10.1.21.23", "Three:10.1.21.33", "Four:10.1.21.23", "Five:10.1.22.23"};
String q = "Two";  //need to find index of element starting with substring "Two"
for (int i = 0; i < items.length; i++) {
    if (items[i].startsWith(q)) {
        System.out.println(i);
    }
}

Your first try does not work because you are trying to get the index of the String ^Two inside your list, but indexOf(String str) does not accept regular expression.

Your second try does not work because matches(String regex) works on the entire String, not just on the beginning.

If you are using Java 8, you could write the following code which returns the index of the first item beginning with "Two", or -1 if none was found.

String[] items = {"One:10.1.22.33", "Two:10.1.21.23", "Three:10.1.21.33", "Four:10.1.21.23", "Five:10.1.22.23"};
String q = "Two";
int index = IntStream.range(0, items.length).filter(i -> items[i].startsWith(q)).findFirst().orElse(-1);

Upvotes: 7

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