java count frequency of characters in a string

1+++METHOD WITH NONDUP+++
2public static String FrequencyOfChars(String str) {
3
4String nonDup = "";
5
6for(int i=0; i < str.length(); i++)
7
8if(!nonDup.contains(""+str.charAt(i)))
9
10nonDup+= ""+str.charAt(i);
11
12 String expectedResult = "";
13
14for( int j=0;j < nonDup.length(); j++) {
15
16int count = 0;
17
18for(int i=0; i < str.length(); i++) {
19
20if(str.charAt(i) == nonDup.charAt(j))
21
22count++;
23}
24
25expectedResult +=nonDup.charAt(j)+"" + count;
26}
27
28return expectedResult;
29}
30
31
32
33+++METHOD WITH REPLACE METHOD+++
34  
35public  static  String  FrequencyOfChars(String str) {
36
37String expectedResult = "";
38
39for( int j=0; j < str.length(); j++) {
40
41int count = 0;
42
43for(int i=0; i < str.length(); i++) {
44
45if(str.charAt(i) == str.charAt(j)) {
46
47count++;
48}
49}
50
51expectedResult +=str.charAt(j)+"" + count;
52
53str = str.replace(""+str.charAt(j) ,  "" ); 
54}
55
56return expectedResult;
57
58}
59
60+++WITH LINKED HASH SET+++
61  public  static  String  FrequencyOfChars(String str) {
62
63String b=new LinkedHashSet<>(Arrays.asList(str.split(""))).toString();
64
65  b = b.replace(", ","").replace("[","").replace("]","");
66
67String result="";
68
69for(int j=0; j<b.length();j++) {
70
71int count=0;
72
73for(int i=0; i<str.length(); i++){
74
75if(str.substring(i, i+1).equals(""+str.charAt(j)))
76
77count++;
78
79}
80
81result+=b.substring(j, j+1)+count;
82
83}
84
85return result;
86
87}
88
89++++LAST METHOD USING COLLECTIONS+++
90  public static String frequency(String str) {
91
92String nonDup="", result="";
93
94for(int i=0; i < str.length(); i++)
95
96if(! nonDup.contains(""+str.charAt(i)))
97
98nonDup += ""+str.charAt(i);
99
100 
101
102for(int i=0; i < nonDup.length(); i++) {
103
104int num = Collections.frequency( Arrays.asList(str.split("") ) ,    ""+nonDup.charAt( i ) );
105
106result += ""+nonDup.charAt(i) + num;
107
108}
109
110 
111
112return result;
113
114}

1public class Frequency   
2{  
3     public static void main(String[] args) {  
4        String str = "picture perfect";  
5        int[] freq = new int[str.length()];  
6        int i, j;  
7          
8        //Converts given string into character array  
9        char string[] = str.toCharArray();  
10          
11        for(i = 0; i <str.length(); i++) {  
12            freq[i] = 1;  
13            for(j = i+1; j <str.length(); j++) {  
14                if(string[i] == string[j]) {  
15                    freq[i]++;             
16                    //Set string[j] to 0 to avoid printing visited character  
17                    string[j] = '0';  
18                }  
19            }  
20        }  
21        //Displays the each character and their corresponding frequency  
22        System.out.println("Characters and their corresponding frequencies");  
23        for(i = 0; i <freq.length; i++) {  
24            if(string[i] != ' ' && string[i] != '0')  
25                System.out.println(string[i] + "-" + freq[i]);  
26        }  
27    }  
28}  

1HashMap<Character, Integer> map = new HashMap<Character, Integer>();
2String s = "aasjjikkk";
3for (int i = 0; i < s.length(); i++) {
4    char c = s.charAt(i);
5    Integer val = map.get(c);
6    if (val != null) {
7        map.put(c, new Integer(val + 1));
8    }
9    else {
10       map.put(c, 1);
11   }
12}