如何遍历字符串数组中的所有字符

Question

I am working a Hash Table project. So I have an array which will hold the Strings. ArrayList<String> buckets = new ArrayList<>();

I want to create a method hash but I am stuck on how to make that method takes in a String and loops over the individual characters in that string and sums their number values all together, and then return the integer sum.

The method hash will use for the test below:

@Test
public void testToString() {
    HashTable h=   new HashTable(10);

    org.junit.Assert.assertEquals( "Empty hash output" ,
             "(0)\t\n"
            +"(1)\t\n"
            +"(2)\t\n"
            +"(3)\t\n"
            +"(4)\t\n"
            +"(5)\t\n"
            +"(6)\t\n"
            +"(7)\t\n"
            +"(8)\t\n"
            +"(9)\t\n"

            , h+""/*.toString()*/
            );
}

@Test
public void hashFunction() {
    HashTable h=   new HashTable(10);

    org.junit.Assert.assertEquals( "hash function test" , 
            4
            , h.hash("abc") % h.size()
            );
    org.junit.Assert.assertEquals( "hash function test backwards string" , 
            4
            , h.hash("cba") % h.size()
            );

Thank you in advances!

Answer 1

There are several ways of doing it - for example, you can use charAt(i) and a for loop:

int sum = 0;
for (int i = 0 ; i != s.length() ; i++) {
    sum += s.charAt(i);
}

You could also convert the string to an array of characters, and use it in a for (char ch : s.toCharArray()) statement, but it would result in an additional memory allocation for the array of characters.

Note 1: you should watch out for numeric overflow.

Note 2: Consider using a different method for computing hash values. Adding up character codes would work, but strings with reordered characters would have identical hash codes.