find the frequency of characters in a string in java
+++METHOD WITH NONDUP+++ public static String FrequencyOfChars(String str) { String nonDup = ""; for(int i=0; i < str.length(); i++) if(!nonDup.contains(""+str.charAt(i))) nonDup+= ""+str.charAt(i); String expectedResult = ""; for( int j=0;j < nonDup.length(); j++) { int count = 0; for(int i=0; i < str.length(); i++) { if(str.charAt(i) == nonDup.charAt(j)) count++; } expectedResult +=nonDup.charAt(j)+"" + count; } return expectedResult; } +++METHOD WITH REPLACE METHOD+++ public static String FrequencyOfChars(String str) { String expectedResult = ""; for( int j=0; j < str.length(); j++) { int count = 0; for(int i=0; i < str.length(); i++) { if(str.charAt(i) == str.charAt(j)) { count++; } } expectedResult +=str.charAt(j)+"" + count; str = str.replace(""+str.charAt(j) , "" ); } return expectedResult; } +++WITH LINKED HASH SET+++ public static String FrequencyOfChars(String str) { String b=new LinkedHashSet<>(Arrays.asList(str.split(""))).toString(); b = b.replace(", ","").replace("[","").replace("]",""); String result=""; for(int j=0; j<b.length();j++) { int count=0; for(int i=0; i<str.length(); i++){ if(str.substring(i, i+1).equals(""+str.charAt(j))) count++; } result+=b.substring(j, j+1)+count; } return result; } ++++LAST METHOD USING COLLECTIONS+++ public static String frequency(String str) { String nonDup="", result=""; for(int i=0; i < str.length(); i++) if(! nonDup.contains(""+str.charAt(i))) nonDup += ""+str.charAt(i); for(int i=0; i < nonDup.length(); i++) { int num = Collections.frequency( Arrays.asList(str.split("") ) , ""+nonDup.charAt( i ) ); result += ""+nonDup.charAt(i) + num; } return result; }