We Keep Coding

Removing full object from a value

Helper Class
public class HomeScreenChatsHelper implements Comparable {
private String ID;
private String Name;
private String Image;
private String From;
private String Seen;
private String LastMessage;
private String LastMessageTime;
public HomeScreenChatsHelper(){
}
public HomeScreenChatsHelper(String id, String name, String image, String from, String seen, String lastmessage, String lastMessageTime) {
this.ID=id;
this.Name = name;
this.Image = image;
this.From = from;
this.Seen = seen;
this.LastMessage = lastmessage;
this.LastMessageTime = lastMessageTime;
}
public String getID() {
return ID;
}
public void setID(String id) {
ID = id;
}
public String getName() {
return Name;
}
public void setName(String name) {
Name = name;
}
public String getImage() {
return Image;
}
public void setImage(String image) {
Image = image;
}
public String getMessage() {
return LastMessage;
}
public void setMessage(String message) {
LastMessage = message;
}
public String getTime() {
return LastMessageTime;
}
public void setTime(String time) {
LastMessageTime = time;
}
public String getFrom() {
return From;
}
public void setFrom(String from) {
From = from;
}
public String getSeen() {
return Seen;
}
public void setSeen(String seen) {
Seen = seen;
}
#RequiresApi(api = Build.VERSION_CODES.KITKAT)
#Override
public int compareTo(Object comparestu) {
long compareage= Long.parseLong(((HomeScreenChatsHelper)comparestu).getTime());
long a = Long.parseLong(LastMessageTime);
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT) {
}
return Long.compare(a,compareage);
}
#Override
public boolean equals(Object o) {
if (this == o) return true;
if (!(o instanceof HomeScreenChatsHelper)) return false;
HomeScreenChatsHelper that = (HomeScreenChatsHelper) o;
return getID().equals(that.getID());
}
#Override
public int hashCode() {
return getID().hashCode();
}
Activity
for(HomeScreenChatsHelper str : mChats) {
if (str.getID().equals(ID)) {
mChats.remove(ID);
break;
}
}
There are a ton of tutorials on how to do it and I've spent the past week looking for a solution and I still don't have it. Is there anyway I can remove an whole object by just specifying just the ID? I wont have the values of all the other fields so I just want to remove a particular object by its ID. Also I cant use the clear option because I need the other data. So can someone help me out please?
With the present code nothing happens. No errors but doesn't work

By using java-8 you can filter the list, result will be the List<HomeScreenChatsHelper> that does have HomeScreenChatsHelper with same id
List<HomeScreenChatsHelper> mChats = new ArrayList<>();
//filter
List<HomeScreenChatsHelper> result = mChats.stream()
.filter(str->!str.getId().equals(Id)).
.collect(Collectors.toList());
Or by using Iterator
// Iterator.remove()
Iterator itr = mChats.iterator();
while (itr.hasNext())
{
HomeScreenChatsHelper x = itr.next();
if (x.getId().equals(Id)) }
itr.remove();
}
}

Your question is quite unclear. is mChats a List containing HomeScreenChatsHelper objects?
I assume so. If this is the case, then you can change your foreach loop into the normal loop
//Assuming mChats is List e.g ArrayList
for (int i = 0; mChats.size(); i++){
if (mChats.get(i).getID().equals(ID)) {
mChats.remove(i);
break;
}
}

The easiest way in Java 8 or later is with Collection#removeIf:
mChats.removeIf(str -> str.getID().equals(ID));
By the way, the convention in Java is for fields to begin with a lowercase letter.

Return object from a list as CustomObject not just raw <T> Object

I have a CustomObject declared as raw type of <T>. And when I populate a List<CustomObject> with new instances of it, I can't get them back as a CustomObject, only as an Object.
public class CustomObject<T> {
private String name;
private T value;
// getters and setters
}
But obviously when I use subclass, all is working as expecting;
public class CustomObject {
private class SubCustomObject<T> {
private String name;
private T value;
}
public CustomObject() {
this.customObject = new SubCustomObject();
private SubCustomObject customObject;
// getters and setters
}
Is there a way to make the first example to behave like the second one, and avoid using extra object and so I could do this:
public class CustomObject<T> {
private String name;
private T value;
private boolean isGroup;
// getters and setters
private void setValue(T value) {
if (value instanceof String) {
this.value = value;
this.isGroup = false;
}
if (value instanceof CustomObject) {
if (isGroup()) {
((List<CustomObject>) this.value).add((CustomObject) value);
} else {
this.value = (T) new ArrayList<CustomObject>();
this.isGroup = true;
setValue(value);
}
}
}
}
public void getItemByName(String name) {
// say the list is already populated
for (CustomObject object : listOfCustomObject) {
String nameField = object.getName();
if (name.equals(nameField) {
System.out.println(nameField);
}
}
}
Instead of this one:
public void getItemByName(String name) {
// say the list is already populated
for (Object object : listOfCustomObject) {
String nameField = ((CustomObject)object).getName();
if (name.equals(nameField) {
System.out.println(nameField);
}
}
}
// Apply that behavior to this and avoid to use inner class.
public class MetadataEntry {
public MetadataEntry() {
this.entity = new Entry();
}
private class Entry<T> {
private String name;
private T value;
private boolean isGroup;
private void setValue(T value) {
if (value instanceof String) {
this.value = value;
this.isGroup = false;
}
if (value instanceof MetadataEntry) {
if (isGroup()) {
((List<MetadataEntry>) this.value).add((MetadataEntry) value);
} else {
this.value = (T) new ArrayList<MetadataEntry>();
this.isGroup = true;
setValue(value);
}
}
}
}
private Entry entity;
public void setName(String name) {
this.entity.name = name;
}
public String getName() {
return this.entity.name;
}
public void setValue(String value) {
entity.setValue(value);
}
public void setValue(MetadataEntry value) {
entity.setValue(value);
}
public boolean isGroup() {
return this.entity.isGroup;
}
public List<MetadataEntity> getChildNodes() {
if (isGroup()) {
return (List<MetadataEntry>) this.entity.value;
}
return null;
}
public String getValue() {
if (!isGroup()) {
return (String) this.entity.value;
}
return null;
}
}

You can not make a list of different types X,Y,Z and put it in a single container of type W. You need to define a bounding parameter on your raw type so that your items and list are of same type. probably your T should be bounded by some interface type or it should extends some class.

Here’s my suggestion. I have abandoned the generics. Instead of just one inner class there is now an abstract inner class with two subclasses, one for groups and one for entries that are not groups. The good news: no cast is necessary anywhere.
public class MetadataEntry {
private String name;
static abstract class Entry {
abstract Entry setValue(String value);
abstract Entry setValue(MetadataEntry value);
abstract boolean isGroup();
abstract List<MetadataEntry> getChildNodes();
abstract String getSimpleValue();
}
static class SimpleEntry extends Entry {
private String value;
public SimpleEntry(String value) {
this.value = value;
}
#Override
Entry setValue(String value) {
this.value = value;
return this;
}
#Override
Entry setValue(MetadataEntry value) {
return new GroupEntry(value);
}
#Override
public boolean isGroup() {
return false;
}
#Override
public List<MetadataEntry> getChildNodes() {
return null;
}
#Override
public String getSimpleValue() {
return value;
}
}
static class GroupEntry extends Entry {
List<MetadataEntry> value;
public GroupEntry(MetadataEntry value) {
this.value = new ArrayList<>();
this.value.add(value);
}
#Override
Entry setValue(String value) {
return new SimpleEntry(value);
}
#Override
Entry setValue(MetadataEntry value) {
this.value.add(value);
return this;
}
#Override
public boolean isGroup() {
return true;
}
#Override
public List<MetadataEntry> getChildNodes() {
return value;
}
#Override
public String getSimpleValue() {
return null;
}
}
private Entry entity;
public void setName(String name) {
this.name = name;
}
public String getName() {
return this.name;
}
public void setValue(String value) {
entity = entity.setValue(value);
}
public void setValue(MetadataEntry value) {
entity = entity.setValue(value);
}
public boolean isGroup() {
return this.entity.isGroup();
}
public List<MetadataEntry> getChildNodes() {
return entity.getChildNodes();
}
public String getValue() {
return entity.getSimpleValue();
}
}
I have used an idea similar to what m 1987 said about a class that returns an instance of itself. I applied it to the inner classes only to free the users of the outer class from caring about this trickery. If you prefer, I am sure it could be applied to the outer class instead. Then you would have an abstrat class on the outer level with two subclasses, and would no longer need the inner classes. This is one of the things you asked for, so you may prefer it, but it comes at a cost: anyone calling setValue() on the outer class would need to remember that they got a new instance back.

I have a CustomObject declared as raw type of <T>.
That doesn't makes sense. You either have a raw type or a generic, not a raw type of a generic.
And when I populate a List with new instances of it, I can't get them back as a CustomObject, only as an Object.
Because your list is not generic (always bad). When you declare a List<Something> it will return Something on a get call. That Something can be generic or a raw type. A List<CustomObject<String>> will not accept a CustomObject<Integer> and using the raw type List<CustomObject> will end in disaster, hence the danger in raw types.
Now let's look at your code. The class
public class CustomObject<T> {
private String name;
private T value;
}
defines an object that behaves the same for any type. In essence what you have here is just a glorified Object with a String serving as its name attached to it.
However, now you do
private void setValue(T value) {
if (value instanceof String)
// ...
if (value instanceof CustomObject)
// ...
}
which separates the behavior for different types. and what happens if the generic type is not a String or a CustomObject?
Let's try to solve your problem. Since generics are meant to unify the behavior, let's look at what the unified behavior is that you're trying to get:
public void getItemByName(String name) {
for (CustomObject object : listOfCustomObject) {
String nameField = object.getName();
// ...
}
}
}
Basically, you require that all the items in listOfCustomObject implement a String getName() method. That's it as far as I can see from your question. That means that your CustomObject<T> should either implement an interface or extend a class (call it Superthing) with that method. Then you will just declare your list as List<? extends Superthing>.
As for the CustomObject itself, it doesn't need to be generic as you hint that there are only 2 types of generics you want to deal with (you have 2 ifs, but no else to deal with a general case). It looks like what you want are 2 different classes with different behaviors that both implement or extend a common supertype.
Try something like this:
abstract class AbstractEntry {
private String name;
protected boolean isGroup;
public void setName(String name) {
this.name = name;
}
public String getName() {
return name;
}
public boolean isGroup() {
return isGroup;
}
}
class MetaEntry extends AbstractEntry {
AbstractEntry value;
MetaEntry(AbstractEntry value) {
this.value = value;
// handle isGroup
}
public void setValue(AbstractEntry value) {
this.value = value;
}
public AbstractEntry getValue() {
if (!isGroup)
return value;
return null;
}
}
class StringEntry extends AbstractEntry {
String value;
StringEntry(String value) {
this.value = value;
isGroup = false;
}
public void setValue(String value) {
this.value = value;
}
public String getValue() {
return value;
}
}

I think there is no need of list as it always hold only one element. As #Ole V.V mentioned, the requirement naturally calls for the use of composition and in fact, generic does not fit into your requirements. Here is how I would tackle your requirements:
public interface Named {
public String getName();
public String getValue();
}
public class CustomObject implements Named {
private String name;
private String value;
private boolean isGroup;
// getters and setters
private boolean isGroup() {
return isGroup;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getValue() {
return value;
}
public void setValue(String value) {
this.value = value;
}
}
public class CustomObject2 implements Named {
private String name;
private CustomObject value;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getValue() {
return value.getValue();
}
public void setValue(CustomObject value) {
this.value = value;
}
}
public class DriverCustomObject {
public static void main(String arg[]) {
CustomObject t = new CustomObject();
t.setName("key1");
t.setValue("value1");
CustomObject2 t2 = new CustomObject2();
t2.setName("complex");
t2.setValue(t);
List<Named> list = new ArrayList<Named>();
list.add(t);
list.add(t2);
for (Named l : list) {
System.out.println(l.getName());
System.out.println(l.getValue());
}
}
}

Return a key-value list, key is attribute and value is attribute's value from other Class

I have a Class A with name and value attributes.
public class A {
private String name;
private String value;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getValue() {
return value;
}
public void setValue(String value) {
this.value = value;
}
}
I have another Class B, such as
public class B {
private String attribute01;
private String attribute01;
private String attribute01;
public String getAttribute01() {
return attribute01;
}
public void setAttribute01(String name) {
this.attribute01 = name;
}
...
}
I would like to return a list with A type, having attribute01 key and where value is getAttribute01() from B, such as ({attribute01, getAttribute01()},{attribute02, getAttribute02()}).
How to implement it?.
Thanks in advance.

Actually I can use a very stupid way, such as
public List<A> keyvalueList(final B objB) {
List<A> list = new ArrayList<>();
A objA = new A();
objA.setName("attribute01");
objA.setValue(objB.getAttribute01());
list.add(objA);
objA = new A();
objA.setName("attribute02");
objA.setValue(objB.getAttribute02());
list.add(objA);
...
return list;
}
Part of them hard coding, obvious it is not a smart way, any proposal.

I wrote sample code for List.Please check my code that is ok to use or not.I added another extra class C.in C,it has two attribute String nameFromA and String attFromB.You should add this C object to list.Following is sample code.
public class A {
private String name;
private String value;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getValue() {
return value;
}
public void setValue(String value) {
this.value = value;
}
}
public class B {
private String att1;
private String att2;
private String att3;
public String getAtt1() {
return att1;
}
public void setAtt1(String att1) {
this.att1 = att1;
}
public String getAtt2() {
return att2;
}
public void setAtt2(String att2) {
this.att2 = att2;
}
public String getAtt3() {
return att3;
}
public void setAtt3(String att3) {
this.att3 = att3;
}
}
public class C {
private String namefromA;
private String attfromB;
public String getNamefromA() {
return namefromA;
}
public void setNamefromA(String namefromA) {
this.namefromA = namefromA;
}
public String getAttfromB() {
return attfromB;
}
public void setAttfromB(String attfromB) {
this.attfromB = attfromB;
}
}
public class Test {
public static void main(String args[]){
C c = new C();
A a = new A();
B b = new B();
a.setName("A1");
b.setAtt1("100");
c.setNamefromA(a.getName());
c.setAttfromB(b.getAtt1());
List list = new ArrayList();
//use generic
list.add(c);
}
}
if you don't want to use class C,then you can use Test class like that
import java.util.ArrayList;
import java.util.List;
public class Test {
private String nameFromA;
private String valueFromB;
public Test(String nameFromA, String valueFromB) {
super();
this.nameFromA = nameFromA;
this.valueFromB = valueFromB;
}
public static void main(String args[]){
A a = new A();
B b = new B();
a.setName("A1");
b.setAtt1("100");
Test test = new Test(a.getName(),b.getAtt1());
List list = new ArrayList();
list.add(test);
}
}
This is my opinion only.Please check it is ok or not.

Sorting int field of the wrapper class spring

I have a Navigation class where I am dynamically creating the navigation I am having two tables folder(it is directory that contains files) and content(it is like files or pages that will render the content on the public site). I have created a Navigation class in which I am having a wrapper class for merging the fields of content into the folder. I have tried using #OrderBy and #OrderColumn but I came to know that it will only work with collections.
List<Folder> folder = folderRepository.findAllByNavDepthLessThanOrderByNavDepthAsc(3);
here I am sorting it with navDepth(this column belongs to Folder entity) I also want to sort it with navOrder(this column belongs to Content entity)
#Service
public class NavigationService {
#Qualifier("jdbcMySQL")
private JdbcTemplate jdbcTemplate;
private FolderRepository folderRepository;
private FolderService folderService;
#Autowired
public NavigationService(JdbcTemplate jdbcTemplate,
FolderRepository folderRepository,
FolderService folderService) {
this.jdbcTemplate = jdbcTemplate;
this.folderRepository = folderRepository;
this.folderService = folderService;
}
#Transactional(propagation=Propagation.REQUIRED, readOnly=false)
public Map<String, NavigationItem> navigationItems() {
// TODO: // CROSS cutting AOP springs
// TODO: http://docs.spring.io/spring/docs/4.2.0.BUILD-SNAPSHOT/spring-framework-reference/htmlsingle/#aop
List<Folder> folder = folderRepository.findAllByNavDepthLessThanOrderByNavDepthAsc(3);
// List<Folder> folder = folderService.navigation();
Map<String, NavigationItem> navItems = new LinkedHashMap<String, NavigationService.NavigationItem>();
for (int i = 0; i < folder.size(); i++) {
NavigationItem ni = new NavigationItem();
ni.setNavDepth((int) (folder.get(i).getNavDepth()));
ni.setFileNamePath(folder.get(i).getDirectoryPath());
ni.setFilepath(folder.get(i).getDirectoryPath());
ni.setChildren(folder.get(i).getContent());
for (int k = 0; k < folder.size(); k++) {
if(folder.get(i).getId() == folder.get(k).getParentId()) {
ni.addSubFolder(folder.get(k));
System.out.println(folder.get(i).getTitle());
System.out.println(folder.get(k));
System.out.println("---!!!!!!________----------!!!!!!!!");
}
}
navItems.put(folder.get(i).getTitle(), ni);
}
return navItems;
}
public class NavigationItem {
private long id;
private long parentId;
private String title;
private String fileName;
private String fileNamePath;
private int navDepth;
private int navOrder;
private String parentFileName;
private String filePath;
private String folderName;
#OrderColumn(name="navOrder ASC")
private List<Content> children = new ArrayList();
private ArrayList<Folder> subFolder = new ArrayList();
public void setSubFolder(ArrayList<Folder> subFolder) {
this.subFolder = subFolder;
}
public String getFilePath() {
return filePath;
}
public void setFilePath(String filePath) {
this.filePath = filePath;
}
public String getFolderName() {
return folderName;
}
public void setFolderName(String folderName) {
this.folderName = folderName;
}
public ArrayList<Folder> getSubFolder() {
return subFolder;
}
public void addSubFolder(Folder subFolder) {
this.subFolder.add(subFolder);
}
public void setChildren(List<Content> list) {
this.children = list;
}
public long getId() {
return id;
}
public void setId(long id) {
this.id = id;
}
public long getParentId() {
return parentId;
}
public void setParentId(long parentId) {
this.parentId = parentId;
}
public String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title;
}
public String getFileName() {
return fileName;
}
public void setFileName(String fileName) {
this.fileName = fileName;
}
public String getFileNamePath() {
return fileNamePath;
}
public void setFileNamePath(String fileNamePath) {
this.fileNamePath = fileNamePath;
}
public long getNavDepth() {
return navDepth;
}
public void setNavDepth(int navDepth) {
this.navDepth = navDepth;
}
public long getNavOrder() {
return navOrder;
}
public void setNavOrder(int navOrder) {
this.navOrder = navOrder;
}
public String getParentFileName() {
return parentFileName;
}
public void setParentFileName(String parentFileName) {
this.parentFileName = parentFileName;
}
public List<Content> getChildren() {
return children;
}
public void addChild(Content child) {
children.add(child);
}
public String getFilepath() {
return filePath;
}
public void setFilepath(String filePath) {
this.filePath = filePath;
}
}
}

Use a Comparator<NavigationItem> and pass that to Collections.sort() or similar methods.
The comparator might look like this:
class NavComparator implements Comparator<NavigationItem> {
int specialValueNoChildren = -1; //assuming nav_order is always 0 or greater
int compare(NavigationItem o1, NavigationItem o2) {
int max1 = getMaxNavOrder( o1 );
int max2 = getMaxNavOrder( o2 );
return Integer.compare( max1, max2 );
}
int getMaxNavOrder( NavigationItem ni ) {
int max = specialValueNoChildren;
for( Content child : ni.getChildren() ) {
max = Math.max(max, child.getNavOrder());
}
return max;
}
}
Here the maximum nav order of all children is selected with -1 being the special case of no children. Then the items are compared by their respective children's maximum nav order.
If you need a different order change that accordingly, e.g. by reversing max1 and max2 or by getting the lowest nav order of the children etc.

Entity Class for ERD

public class Table{
private String column[];
private String dataType[];
private boolean PK[];
private boolean NN[];
private int count;
public Table()
{
count =0;
}
public void AddColumn(String name,String dtype,boolean pk,boolean nn)
{
column[count]=name;
dataType[count]=dtype;
PK[count]=pk;
NN[count]=nn;
count++;
}
public void Display(Table T)
{
}
public void DeleteColumn(String name)
{
if(count==0){return;}
else if(count ==1)
{
if(name==column[0])
column[0]=null;
dataType[0]=null;
count--;
return;
}
else
for(int i=0;i<count;i++)
{
if(name==column[i])
{
column[i]=column[count-1];
dataType[i]=dataType[count-1];
PK[i]=PK[count-1];
NN[i]=NN[count-1];
}
}
}
This is my table class; as im designing an Entity table and for keeping column Name data type etc. Is this class and its private attributes correct or should i break this into more classes eg attributes.

I think that you should create Column class.
I will do it in this way (of course it can be done better):
public class DataType {
public static String DATA_TYPE_1 = "dataType1";
public static String DATA_TYPE_2 = "dataType2";
public static String DATA_TYPE_3 = "dataType3";
}
public class Column() {
private String name;
private DataType dataType;
private boolean PK;
private boolean NN;
// getters and setters
}
public class Table {
private ArrayList<Column> columns;
public Table() {
columns = new ArrayList<Column>();
}
public boolean AddColumn(Column column) {
columns.add(column);
}
public boolean DeleteColumn(String name) {
for (Column c : columns) {
if (c.getName().equals(name)) {
return columns.remove(column);
}
}
return false;
}
}