How to find an index of given String in array of strings?

You can use Guava, then your code can looks like this

String[] stringArray = {"s1", "s2", "s3"};

int index = Iterators.indexOf(Iterators.forArray(stringArray), new Predicate<String>() {
    @Override
    public boolean apply(String input) {
        return input.equals("s2");
    }
});

or simpler

int index = Arrays.asList(stringArray).indexOf("s2");

Your code can also look like this

public class Finder {

    private String[] stringArray = {"s1", "s2", "s3"};

    public int findIndex(String name) {
        for (int i = 0; i < stringArray.length; i++) {
            if (stringArray[i].equals(name))
                return i;
        }

        throw new RuntimeException("Not found");
    }

    public static void main(String... s) {
        int index = new Finder().findIndex("s1");

        System.out.println(index);
    }
}

You can either run your code through a debugger and find out why it doesn't work, or add some println traces to your original code and you'll see what the problem is:

public long myFunc(String name) throws Exception {
    System.out.println("Looking for: " + name);
    for (int i = 0; i < amount; i++){
        if(this.otherString[i].equals(name))
            return longArray[i];
        System.out.printf("%4d: \"%s\": No match.%n", i, this.otherString[i]);
    }
    for (int i = amount; i < this.otherString.length; i++)
        System.out.printf("%4d: \"%s\": Not checked.%n", i, this.otherString[i]);
    throw new Exception("Not found");
}

By the way, make sure you are correctly interpreting the method's behaviour. Could it be that it's finding it but throwing an ArrayIndexOutOfBoundsException because i is greater than longArray.length, and you misinterpret that as the exception you are explicitly throwing?

This might be completely wrong, but isn't the problem just missing curly brackets in the if statement? I am new to the java language and the example is probably messy, but it uses the same structure from your question and works just fine:

public class random_class {

public static void main(String[] args) {
    // TODO Auto-generated method stub
    String[] a = new String[] {"hi!", "hello world!", "ho ho ho world!"};       
    int b = getHWIndex(a);
    System.out.println(b);
}

public static int getHWIndex(String[] stringArray){
    int i;
    Boolean test = false;
    for(i=0;i<stringArray.length;i++){
        if(stringArray[i].equals("hello world!")){
            test = true;  
            break;
        }
    }
    if(test == true){
    return i;}else{
        return i = 0; // this is not a good answer... 
//but as you return an int I could not think on a quick way to fix   the return when there is no match.
        }
    }
}