Puge -- understanding of getordefault() method

analysis getOrDefault() Method

Introduce

getOrDefault(Object key, V defaultValue)
In operation Map When the collection , Determine whether this is stored key. If there is a corresponding value value , If it does not exist , Then the user-defined default value is returned defaultValue value .

Code implementation

LeetCode The first 387 topic ： The first unique character in the string

 public static void main(String[] args) {
    
        String s = "loveleetcode";
        System.out.println(firstUniqChar(s));
    }
    public static int firstUniqChar(String s) {
    
        Map<Character, Integer> frequency = new HashMap<Character, Integer>();
        for (int i = 0; i < s.length(); ++i) {
    
            char ch = s.charAt(i);
            //  When this key when , Just use this value value , There is no default defaultValue
            frequency.put(ch, frequency.getOrDefault(ch, 0) + 1); //  Put the previous values in , By default +1 Calculation , Press... Only when there is a repetition ch Of value Calculation .
        }
        for (int i = 0; i < s.length(); ++i) {
    
            if (frequency.get(s.charAt(i)) == 1) {
     //  Returns the specified character , Treat characters as key Go back 
                return i;
            }
        }
        return -1; //  Returns the last value 
    }

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The end