Find the frequency of each character in a String

To find the frequency of each character in a String you can take help of a HashMap or Hashtable.
Below is the code for the same:

public class Manager{
    public static void main(String[] args) {
    	String str="ABCD abcd";
    	Map<Character, Integer> occurences=new HashMap<>();
    	for(char character: str.toCharArray()) {
    		Integer count=occurences.get(character);
    		if(count == null) {
    			count = 0;
    		}
    		count++;
    		occurences.put(character, count);
    	}    	
    	System.out.println(occurences);    	
	}   
}

Find the lowest/highest frequency of characters in a string using java:

You can add 2 more block of code- one to find the lowest and highest number in map and one to print the desired item. The above code is rewritten as well:

public class Manager {		
	public static void main(String[] args) {
		
		String str="my name is Prasanna";
        
        Map map=new LinkedHashMap();        
        char[] arr=str.toCharArray();
        for(int i=0;i<arr.length;i++) {
            Integer value=(Integer)map.get(arr[i]);
            if(value == null) {
                map.put(arr[i], 1);
            }else {
                value++;
                map.put(arr[i], value);
            }            
        }
        System.out.println("Frequency of each character : "+ map);
        
        //find the min and max frequency in the map:
        Integer minValue=1;
        Integer maxValue=1;
        for(Object key: map.keySet()){
            Integer value=(Integer)map.get(key);
            if(value > maxValue)
                maxValue=value;
            else
                minValue=value;
        }
        System.out.println("Min frequency: "+minValue);
        System.out.println("Max frequency: "+maxValue);
        
        for(Object key: map.keySet()){
            Integer value=(Integer)map.get(key);
            if(value == minValue) {
                System.out.println("First item having lowest frequency : " + key);
                break;            
            }                        
        }
    }  
}