CODEWITHSUNDEEP
javaarraysobjectjava-8
Santos
Santos

Reputation: 71

How to convert Object's property values in to an array in Java?

Say if I have, a list of objects like:-

[id = 1, age = 34, name = "abc"]
[id = 2, age = 34, name = "xyz"]
[id = 3, age = 34, name = "mno"]

then I need to convert them to :-

[1], [34], [abc],
[2], [34], [xyz],
[3], [34], [mno]

Upvotes: 2

Views: 4144

Answers (3)

MichałF
MichałF

Reputation: 21

In this case you can use streams with map and flatMap methods:

public static void main(String[] args) {
    MyClass obj = new MyClass(1, 50, "John");
    MyClass obj2 = new MyClass(2, 30, "Michał");
    List<MyClass> list = Arrays.asList(obj, obj2);
    List<Object> all = list.stream()
            .map(o -> Arrays.asList(o.getId(), o.getAge(), o.getName()))
            .flatMap(Collection::stream)
            .collect(Collectors.toList());

    all.forEach(element -> System.out.println(element));
}

public static class MyClass {
    private final int id;
    private final int age;
    private final String name;

    public MyClass(int id, int age, String name) {
        this.id = id;
        this.age = age;
        this.name = name;
    }

    public int getId() { return id; }
    public int getAge() { return age; }
    public String getName() { return name; }
}

Upvotes: 2

S. Kadakov
S. Kadakov

Reputation: 919

Say, you have class Person:

package stack.overflow.atest;

public class Person {
    int id;
    int age;
    String name;

    public Person(int id, int age, String name) {
        this.id = id;
        this.age = age;
        this.name = name;
    }
}

As of Java 8 you can do something like this:

List<Object> result = Stream
        .of(new Person(1, 23, "aaa"), new Person(2, 34, "bbb"))
        .flatMap(p -> Stream.of(p.id, p.age, p.name))
        .collect(Collectors.toList());

System.out.println("result: " + result);

this produces:

result: [1, 23, aaa, 2, 34, bbb]

Upvotes: 0

user15309136
user15309136

Reputation:

You can convert each Object to an array of its fields Object[] as follows:

public static void main(String[] args) throws Exception {
    List<Person> people = List.of(
            new Person(1, 34, "abc"),
            new Person(2, 34, "xyz"),
            new Person(3, 34, "mno"));

    Object[][] arr = people.stream()
            .map(person -> new Object[]{
                    person.getId(), person.getAge(), person.getName()
            }).toArray(Object[][]::new);

    // output
    Arrays.stream(arr).map(Arrays::toString).forEach(System.out::println);
    //[1, 34, abc]
    //[2, 34, xyz]
    //[3, 34, mno]
}

static class Person {
    int id;
    int age;
    String name;

    public Person(int id, int age, String name) {
        this.id = id;
        this.age = age;
        this.name = name;
    }

    public int getId() { return id; }
    public int getAge() { return age; }
    public String getName() { return name; }
}

Upvotes: 1

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