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Unable to get desired output in "Predicate" "and" of Java

I have the following class Person -
Person.java -
public class Person {
private int id;
private String department;
private double salary;
public Person(int id, String department, double salary) {
this.id = id;
this.department = department;
this.salary = salary;
}
public String getDepartment() {
return department;
}
public double getSalary() {
return salary;
}
#Override
public String toString() {
return "Person{" +
"id=" + id +
", department='" + department + '\'' +
", salary=" + salary +
'}';
}
}
It has the fields -
id, department, salary
Now I have first predicate -
Predicate<List<Person>> hasSalaryOf40k = list -> {
boolean myReturn = false;
Iterator<Person> iterator = list.iterator();
while (iterator.hasNext()) {
Person person = iterator.next();
double salary = person.getSalary();
if (salary == 40000) {
myReturn = true;
break;
}
}
return myReturn;
};
Here, I want to filter out those lists having persons with salary as 40K.
Second predicate -
Predicate<List<Person>> isDeveloper = list -> {
boolean myReturn = false;
Iterator<Person> iterator = list.iterator();
while (iterator.hasNext()) {
Person person = iterator.next();
String department = person.getDepartment();
if (department.equals("Developer")) {
myReturn = true;
break;
}
}
return myReturn;
};
Here, I want to filter out those lists having persons with department as 'developer'
Third predicate -
Predicate<List<Person>> hasSalaryOf40kAndIsDeveloper = list ->
hasSalaryOf40k.and(isDeveloper).test(list);
Here, I want to filter out those lists having persons with both salary as 40K and department as "developer"
Now I have the following two lists -
List<Person> list1 = new ArrayList<>(List.of(
new Person(1, "Developer", 35000),
new Person(2, "Accountant", 40000),
new Person(3, "Clerk", 20000),
new Person(4, "Manager", 50000)
));
List<Person> list2 = new ArrayList<>(List.of(
new Person(1, "Developer", 40000),
new Person(2, "Accountant", 35000),
new Person(3, "Clerk", 22000),
new Person(4, "Manager", 55000)
));
The list1 does not match the desired criteria while list2 matches the desired criteria.
Now I call the predicate method test -
System.out.println(hasSalaryOf40kAndIsDeveloper.test(list1));
System.out.println(hasSalaryOf40kAndIsDeveloper.test(list2));
Output -
true
true
Desired output -
false
true
Where am I going wrong and how to correct my code?

You're applying the predicate to the whole list and not each element of the list, so it's true that the list contains a developer and its true that the list contains a salary over 40k. You need to apply the predicate to the Person object rather than the List<Person> object

How can I duplicate an HashMap with duplicate values

I need to create new HashMaps that contain only the duplicate values of my first HashMap :
Original map: {Player1=Hello, Player2=Hi, Player3=Hi, Player4=Hello, Player5=Hello}
For the outputs, I want to get :
Hello map: {Player1=Hello,Player4=Hello, Player5=Hello}
Hi map: {Player2=Hi, Player3=Hi}
What is best way to do?

If you are using Java8+ you can use stream, with groupingBy and toMap like so :
Map<String, Map<String, String>> collect = map.entrySet().stream()
.collect(Collectors.groupingBy(Map.Entry::getValue,
Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue)));
For e simple map, your outputs can be :
Hi - {Player2=Hi, Player3=Hi}
Hello - {Player5=Hello, Player1=Hello, Player4=Hello}
Ideone demo

class Player {
private String name;
private int id;
public Player(int id) {
this.id = id;
this.name = "Player " + id;
}
#Override
public int hashCode() {
return this.id;
}
#Override
public String toString() {
return this.name;
}
}
Player[] players = new Player[5];
IntStream.range(0, players.length).forEach(i -> players[i] = new Player(i + 1));
// -------------------------------------------------------------------------
HashMap<Player, String> original = new HashMap<>();
original.put(players[0], "Hello");
original.put(players[1], "Hi");
original.put(players[2], "Hi");
original.put(players[3], "Hello");
original.put(players[4], "Hello");
HashMap<String, HashMap<Player, String>> duplicates = new HashMap<>();
original.keySet().stream().forEach(key -> {
String value = original.get(key);
HashMap<Player, String> duplicate = duplicates.get(value);
if (duplicate == null) {
duplicate = new HashMap<>();
duplicates.put(value, duplicate);
}
duplicate.put(key, value);
});
System.out.println("Original: " + original);
duplicates.forEach((key, value) -> {
System.out.println(key + ": " + value);
});
//
Original: {Player 1=Hello, Player 2=Hi, Player 3=Hi, Player 4=Hello, Player 5=Hello}
Hi: {Player 2=Hi, Player 3=Hi}
Hello: {Player 1=Hello, Player 4=Hello, Player 5=Hello}

Reduce list of object into Immutable map with lambda

I have a list of Person object. All person has a unique id, but the person's name can be the same.
Person {
String id,
String name,
}
I want to convert this array of persons into ImmutableMap<String, ImmutableSet<String>>. The key of the map should be the user's name, the immutable set contains the ids of specific user's name.
I know how to do it using HashMap and HashSet:
for (person : personList) {
String id = person.id;
String name = person.name;
if (!hashMap.containsKey(name)) {
hashMap.put(name, new HashSet<String>());
}
hashMap.get(name).add(id);
}
I want to know how to do it using ImmutableMap, ImmutableSet with lambda.

Here is one possible solution.
First, generate some data. Three names and 18 ids. Put them in a list.
Random r = new Random();
int[] ids = r.ints(1000, 1, 1000).distinct().limit(18).toArray();
int id = 0;
List<Person> people = new ArrayList<>();
for (int i = 0; i < 6; i++) {
for (String name : List.of("Bob", "Joe", "Mary")) {
people.add(new Person(name, ids[id++]));
}
}
Now creating the map.
Use groupingBy to create a key pointing to a collection. The key is the
name and the collection is the map.
The collection(a set) holds the ids
Map<String, Set<Integer>> nameToID =
Collections.unmodifiableMap(people.stream().collect(
Collectors.groupingBy(Person::getName, Collectors.mapping(
Person::getID, Collectors.toUnmodifiableSet()))));
Print them.
nameToID.entrySet().forEach(
e -> System.out.println(e.getKey() + " -> " + e.getValue()));
}
}
Here is the Person class with some additional methods and a constructor.
class Person {
String name;
int id;
public Person(String name, int id) {
this.name = name;
this.id = id;
}
public String getName() {
return name;
}
public int getID() {
return id;
}
public String toString() {
return "(" + name + "," + id + ")";
}
}

Get all first value of List<Object[]>

how can I retrieve only the pet types using lambda expression? I want a new list containing only "dog", "cat", etc,
I have list:
List<Object[]> list;
in this list I have structure:
list.get(0) returns ("dog", 11)
list.get(1) returns ("cat", 22)
etc.
how can I retrieve only the pet types using lambda expression? I want a new list containing only "dog", "cat", etc,

An easy way is the use of the stream api:
List firstElements = list.stream().map(o -> o[0]).collect(Collectors.toList());

It is as simple as using map and collect.
private void test(String[] args) {
List<Animal> list = new ArrayList<>();
list.add(new Animal("dog",11));
list.add(new Animal("cat",22));
List<String> names = list.stream()
// Animal -> animal.type.
.map(a -> a.getType())
// Collect into a list.
.collect(Collectors.toList());
System.out.println(names);
}
I used Animal as:
class Animal {
final String type;
final int age;
public Animal(String type, int age) {
this.type = type;
this.age = age;
}
public String getType() {
return type;
}
public int getAge() {
return age;
}
#Override
public String toString() {
return "Animal{" +
"type='" + type + '\'' +
", age=" + age +
'}';
}
}

using iterator to go over list of hashmaps

I have a String exp, which I have to compare with the mapsList.
String exp = "nodeId=1&&name=Router||level=1";
List mapList = new ArrayList();
Map map = new HashMap();
map.put("nodeId","1");
map.put("name","Router");
map.put("level", "1");
Map map1 = new HashMap();
map1.put("nodeId","2");
map1.put("name","Router");
map1.put("level","2");
Map map2 = new HashMap();
map2.put("nodeId","3");
map2.put("name","Router");
map2.put("level","3");
mapList.add(map);
mapList.add(map1);
mapList.add(map2);
I take the exp and split into an array.
String delims = "[\\&&\\||\\=]+";
String[] token = exp.split(delims);
Then I divide the array into two smaller sub arrays. One for Keys and the other for values. After which I compare ...
if(map.keySet().contains(a1[0]) && map.keySet().contains(a1[1]) || map.keySet().contains(a1[2])){
if(map.values().contains(a2[0]) && map.values().contains(a2[1]) || map.values().contains(a2[2])){
System.out.println("Match\tMapKeys: "+map.keySet()+" Values: "+map.values());
}else{
System.out.println("No Match\t");
}
}
So my problem is I can do this for each map, but can't figure out how to implement it with iterator.
Can some1 push me in the right direction?
Thanks.

You really, really want to define an object to hold your data, instead of using HashMaps.
class Node {
private int id;
private String name;
private int level;
public Node(int id, String name, int level) {
this.id = id;
this.name = name;
this.level = level;
}
public int getId() {
return id;
}
public String getName() {
return name;
}
public int getLevel() {
return level;
}
}
now you populate the list like this
List<Node> nodeList = new ArrayList<Node>();
nodeList.add(new Node(1, "Router", 1));
nodeList.add(new Node(2, "Router", 2));
nodeList.add(new Node(3, "Router", 3));
and you could look for your match like this
String exp = "nodeId=1&&name=Router||level=1";
String delims = "[\\&&\\||\\=]+";
String[] token = exp.split(delims);
int id = Integer.parseInt(token[1]);
String name = token[3];
int level = Integer.parseInt(token[5]);
boolean match = false;
for (Node node : nodeList) {
if (node.getId() == id && node.getName().equals(name)
&& node.getLevel() == level) {
System.out.println("Match found: " + node);
match = true;
}
}
if (!match) {
System.out.println("No match");
}
which gives me the following output
Match found: Node#1391f61c
and the next step is to implement toString.
You should check out http://docs.oracle.com/javase/tutorial/java/concepts/ as it introduces objects and why they are useful.