Suppose the following is our string -
String myStr = "thisisit";
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To count the number of occurrences, we use a HashMap. Loop and use containsKey(0 and charAt() methods to count the number of occurrences of each character in the above string -
HashMap hashMap = new HashMap<>(); for (int i = myStr.length() - 1; i >= 0; i--) { if (hashMap.containsKey(myStr.charAt(i))) { int count = hashMap.get(myStr.charAt(i)); hashMap.put(myStr.charAt(i), ++count); } else { hashMap.put(myStr.charAt(i),1); } }
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Example
The following is the program to count the number of occurrences of each character-
import java.util.HashMap; public class Demo { public static void main(String[] args) { String myStr = "thisisit"; System.out.println("String ="+myStr); HashMap
hashMap = new HashMap<>(); for (int i = myStr.length() - 1; i >= 0; i--) { if (hashMap.containsKey(myStr.charAt(i))) { int count = hashMap.get(myStr.charAt(i)); hashMap.put(myStr.charAt(i), ++count); } else { hashMap.put(myStr.charAt(i),1); } } System.out.println("Counting occurrences of each character = "+hashMap); } }
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Output
String =thisisit Counting occurrences of each character = {s=2, t=2, h=1, i=3}
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