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get string using stream api

I have following code :
private String categoryId;
List<Category> categories = new List<>();
for(String category:categories){
if(category.getName().equals(categoryName)){
categoryId = category.getId();
break;
}
}
I want to use stream api here to get categoryId. My category class as follows.
class Category{
private String name;
private String id;
// gettters and setters.
}
category Id is assigned randomly when a new category is created.
Thanks in advance.

try to use this :
categoryId = categories.stream()
.filter(category -> category.getName().equals(categoryName))//filter by name
.map(Category::getId) //get only the ids
.findFirst() //return just the first result
.orElse(null); //if no result then return null

If you want to use Streams, you can write:
categories.stream().filter(c -> {
if (c.getName().equals(categoryName)) categoryId = c.getId()});

java ArrayList with two columns

I have to update a table with two columns and I have created a class
public class Country {
private String url;
private String search;
public Country(String url, String search) {
this.url = url;
this.search = search;
}
// ...
}
List<Country> countries = new ArrayList<Country>();
countries.add(new Country(urls, txt));
...
Countries has a data {java.com.main#yfxse34567}
Could be {www.google.com, main string...}
How can I put a proper data into countries list

Override the toString() method
Example
List<Country> countries = new ArrayList<Country>() {
#Override
public String toString() {
String result = "{";
for (int index= 0; index < size(); index++){
result = result.concat(this.get(index).url);
if (index != size()-1) {
result = result.concat(", ");
}
}
result = result.concat("}");
return result;
}
};

For me your solution should work, however try to instantiate the parent first and then add the instance ... Something like
Country instanceCountry = new Country();
instanceCountry.setUrl("www.google.com");
instanceCountry.setSearch("xpto");
countries.add(instanceCountry);
Do not forget to generate the Getters and Setters

Java - String NullPointerException

I'm making a mysql database connector with java to show all the data.
When I run the code, I get an NullPointerException in my getData() function.
here is my code.
public String[][] getData() {
String values[][];
try {
rs = st.executeQuery("SELECT * FROM adresses");
int i = 0;
while(rs.next()) {
String id = rs.getString("id");
String name = rs.getString("name");
String adress = rs.getString("email_adress");
String catagory = rs.getString("catarogy");
values[i][0] = id;
values[i][1] = name;
values[i][2] = adress;
values[i][3] = catagory;
i++;
}
return values;
} catch (SQLException e) {
e.printStackTrace();
return values;
}
}
When the value of the String values is nothing I get The error. But if I give the String allready a value it says nothing .
public String[][] getData() {
String values[][] = {{"","","",""},
{"","","",""},
{"","","",""},};
try {
rs = st.executeQuery("SELECT * FROM adresses");
int i = 0;
while(rs.next()) {
String id = rs.getString("id");
String name = rs.getString("name");
String adress = rs.getString("email_adress");
String catagory = rs.getString("catarogy");
values[i][0] = id;
values[i][1] = name;
values[i][2] = adress;
values[i][3] = catagory;
i++;
}
return values;
} catch (SQLException e) {
e.printStackTrace();
return values;
}
}
I want more data than that in my data String. how can I let it automatically do that??
Tnx.
PS.
The function is called in my class FrameGUI and has to change to Object
public class FrameGUI extends JFrame {
public JTable dataHolder;
Mysql mysql = new Mysql();
public String[] columnNames = {
"ID", "Name", "Adress", "Catagory"
};
-> public Object[][] data = mysql.getData();
public FrameGUI() {
init();
mysql.getData();
}
}

You do not initialize String values[][] so it is null. You either need to initialize it first or use a more appropriate datastructure like a List.

You should define a class and use a List (e.g. the ArrayList) instead.
e.g. if you want to call it User -
public class User {
private String id;
private String name;
//...
}
and a list
List<User> users = new ArrayList<User>();
and then instantiate the User class for each row and add the new instance to the list -
User currUser = new User();
users.add(currUser);
//set values from result set
The list can grow automatically when needed and the code is much more readable than using the array.

You get an index out of bounds in the first example because a String[][] (or String Matrix) gets initialized as a zero-length array.
In the second instance, you initialized the array to a size of 3x4 - that works so long as you only get 3 results back.
What you really need is a data structure with a dynamic size. Arrays aren't automatically sized dynamically. Try using a collection implementation like ArrayList or LinkedList or Vector.
Also, instead of saving your values to a String[], try creating a bean class that can hold your result. Create a new instance of it for each result that you get back instead of initializing a new array.

Because you didn't initialized your array, that is why you get NPE. Actually I suggest you to use List for your purposes:
public ArrayList<ArrayList<String>> getData() {
ArrayList<ArrayList<String>> values = new ArrayList<>();
try {
rs = st.executeQuery("SELECT * FROM adresses");
while(rs.next()) {
String id = rs.getString("id");
String name = rs.getString("name");
String adress = rs.getString("email_adress");
String catagory = rs.getString("catarogy");
ArrayList<String> list = new ArrayList<>();
list.add(id);
list.add(name);
list.add(adress);
list.add(catagory);
values.add(list);
}
return values;
} catch (SQLException e) {
e.printStackTrace();
return null;
}
}

The main problem in you code is you are using arrays to save variable number of data. Arrays is fixed sized after they are created so you can't add (or remove) elements to them dynamically.
Instead of using arrays you should use an ArrayList object which have methods to add more elements. Also instead of creating a multidimensional array it looks like a better idea to create a class for the data you get from you database.
So lets first create a Address class:
public class Address {
public String id, name, adress, catagory;
public Address(String id, String name, String adress, String catagory) {
this.id = id;
this.name = name;
this.adress = adress;
this.catagory = catagory;
}
}
Now you can write you code as:
public List<Address> getData() {
List<Address> values = new ArrayList<Address>();
try {
rs = st.executeQuery("SELECT * FROM adresses");
int i = 0;
while(rs.next()) {
String id = rs.getString("id");
String name = rs.getString("name");
String adress = rs.getString("email_adress");
String catagory = rs.getString("catarogy");
values.add(new Address(id, name, adress, catagory));
}
return values;
} catch (SQLException e) {
e.printStackTrace();
return values;
}
}
The returned list will contain a list of Address objects which have the values from you database. Also, the size of the list is always the same as the content you put into it.

How to map a class via jdbc template

A table contains three columns: Order, Item and price which i access via Jdbc Template and trying to map with DTO.
Order Item Price
101 "xyz" 100
101 "Pqr" 150
101 "abc" 125
102 "any" 200
102 "one" 101
I can map the above table with my dto with as below,
public class myDTO{
String Order; // Order number
String Item; // item name
String price; // item price
//getter-setter below
}
But i want to map the table in such a way where i would able to link an order against all Items and price which has common Order Number. I am just giving a plain idea of expected DTO class but not able to map.
public class requiredDTO{
String order;
List<String> value;
List<String> price;
//getter setter below
}

Use 'BeanPropertyRowMapper' your columns name must match property names of MyDTO.
getJdbcTemplate().query("SELECT Order, Item, Price FROM your_table", new BeanPropertyRowMapper(MyDTO.class));
Then i recommend you to do your group logic later in java.
Good Luck!

You don't want either of your solutions... What you want (IMHO is the following)
public class Order {
private long id;
private Set<Item> items;
}
public class Item {
private String name;
private long price;
}
Use a ResultSetExtractor to create the List<Order>.
public OrderResultSetExtractor implement ResultSetExtractor<List<Order>> {
public List<Order> extractData(ResultSet rs) throws SQLException, DataAccessException {
List<Order> orders = new ArrayList<Order>();
Order current = null;
while (rs.next()) {
long orderId = rs.getLong(1);
String itemName = rs.getString(2);
long price = rs.getLong(3);
if (current == null || current.getId() != orderId) {
current = new Order();
current.setId(orderId);
orders.add(current);
}
current.getItems().add(new Item(itemName, price));
}
return orders;
}
}
Something along these lines.

removing duplicate records in list

Hi while developing one of my web application i am storing the user information in to an ArrayList based on sql query executed, it contain duplicate objects how to remove duplicate objects in list , i already tried some method but it still not working.
This Is My Code Correct me where i am wrong
public ArrayList loadData() throws ClassNotFoundException, SQLException {
ArrayList userList = new ArrayList();
String url = "";
String dbName = "";
String userName = "";
String password = "";
Connection con = null;
Class.forName("org.apache.derby.jdbc.ClientDriver");
con = DriverManager.getConnection(url + dbName, userName, password);
PreparedStatement ps = null;
try {
String name;
String fatherName;
int Id;
String filePath;
int age;
String address;
String query = "SELECT NAME,FATHERNAME,AGE,ADDRESS,ID,FILEPATH FROM USER_INFORMATION ,USER_PHOTO WHERE ID=USER_ID";
ps = con.prepareStatement(query);
ResultSet rs = ps.executeQuery();
while (rs.next()) {
name = rs.getString(1);
fatherName = rs.getString(2);
age = rs.getInt(3);
address = rs.getString(4);
Id = rs.getInt(5);
filePath=rs.getString(6);
/* if(flag)
{
prev=Id;
flag=false;
}
else if(Id==prev)
{
TEMP=TEMP+";"+filePath;
}*/
//PhotoList = PhotoList(Id, con);
UserData list = new UserData();
list.setName(name);
list.setFatherName(fatherName);
list.setAge(age);
list.setAddress(address);
list.setId(Id);
// list.setFilePath(filePath);
userList.add(list);
}
ps.close();
con.close();
} catch (Exception e) {
e.printStackTrace();
}
ArrayList al = new ArrayList();
HashSet hs = new HashSet();
hs.addAll(userList);
al.clear();
al.addAll(hs);
return al;
}
And My Bean Class contant is
public class UserData {
private String name;
private String fatherName;
private int Id;
//private String filePath;
private int age;
private String address;
public UserData()
{
}
public UserData(String name, String fatherName,int Id, int age,String address)
{
this.name = name;
this.fatherName = fatherName;
this.Id = Id;
//this.filePath=filePath;
this.age=age;
this.address=address;
}
//GETTER AND SETTER..

General Idea: Use Set, not List. But you must override hash and equals of the class.

If you want a Collection of objects that does not have a specific order and you don't want duplicates, it's better for you just to use a Set like for example HashSet, or, if in your set the order is important, the TreeSet.
Just remember to override the hash and equals methods.
if you add this to your bean everything should work:
public int hashCode() {
return (name + fatherName+ Id + filePath + age + address).hashCode();
}
public boolean equals(Object obj) {
return ( hashCode() == obj.hashCode() );
}

Your userdata class does not implement equals or hashcode. This means two instances created with the same values will not be counted as duplicates. This is why the set contains duplicates.
For example
UserData u1 = new UserData("Foo", "bar",1, 1,"baz");
UserData u2 = new UserData("Foo", "bar",1, 1,"baz");
u1 and u2 are not considered equal as they are different objects. Adding an equals and hashcode method should fix this. However even better is adarshr's idea of removing dupes in the SQL.

All duplicates must be removed at an SQL level. Your SQL is suggesting that it could be generating duplicate records.
String query = "SELECT NAME,FATHERNAME,AGE,ADDRESS,ID,FILEPATH FROM USER_INFORMATION ,USER_PHOTO WHERE ID=USER_ID";
What does the clause ID = USER_ID mean? Shouldn't you be passing in that value as an input to your query?
Also, is the column ID a primary key? Otherwise, use a where clause that doesn't generate duplicates.