java - Dont know why I am getting a NullPointerException -

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• what nullpointerexception, , how fix it? 12 answers

i have inputted data array c_pid[] database. i'm trying run loop. if the value array not null loop should carry on. seems run fine. getting desired output. 1 problem have reason showning me nullpointer exception.

i have provided code screenshot down below.enter image description here

i trying run loop

while(!c_pid[cnt].equals(null)){ 

after im getting java.lang.nullpointerexception error

<%@page import="storage.data"%> <%@ taglib prefix="fn" uri="http://java.sun.com/jsp/jstl/functions" %> <%     string[] c_pid = new string[100000];     string c = "", pna = "", pty = "", ppr = "", stock = "", imgpath = "";     //string mylist = new string[10];     int = 0, d = 0;     int result = 0, count = 0;     int setres;     int[] arr = new int[100000];     string testval = "75";     int item_id = 0;     data dt = new data();     string item = "", cartid = "", user = "";     string[] prdid = new string[60];     int cnt = 0;      try {         dt.st = dt.cn.createstatement();         string select_match = "select user_prod_id, count(*) rep "                 + "from cart_table "                 + "group user_prod_id "                 + "order rep desc";         dt.rs = dt.st.executequery(select_match);          while (dt.rs.next()) {             //prdid[a] = dt.rs.getstring("user_prod_id");             //a=a+1;             c_pid[cnt] = dt.rs.getstring("user_prod_id");             cnt = cnt + 1;         }         out.println("<br/>---------xxx--------");         string select3 = "select "                 + "product_table.p_id,product_table.p_type,"                 + "product_type.pt_id,"                 + "product_table.p_name,product_table.imgpath,product_table.p_price,product_table.stock,product_table.add_date,"                 + "product_type.pt_name "                 + "from product_table "                 + "inner join product_type "                 + "on product_table.p_type=product_type.pt_id "                 + "order product_table.add_date desc"                 + "";         cnt = 0;         int size = c_pid.length;         out.println("size of array " + size + "<br />");         while (!c_pid[cnt].equals(null)) {             out.println(c_pid[cnt] + "<br />");              cnt = cnt + 1;         }     } catch (exception ex) {         ex.printstacktrace();         out.println(ex);     }        %> 

the problem in loop instead loop until array[index] == null while (!c_pid[cnt].equals(null)) { have loop until end of array.

suggest

instead of using :

string[] c_pid = new string[100000]; 

you can use list instead, standard , don't need initialize max number open size :

list<string> c_pid = new arraylist<>(); ... c_pid.add(dt.rs.getstring("user_prod_id")); ... out.println("size of array " + c_pid.size() + "<br />"); .... out.println("size of array " + c_pid.size() + "<br />"); (string str : c_pid) {     out.println(str + "<br />"); }