how to initialize static ArrayList in one line

Question

i have MyClass as

MyClass(String, String, int);

i know about how to add to add to ArrayList in this way:

MyClass.name = \"N         


        

Answer 1

You can do

List<MyClass> list = Arrays.asList(
                         new MyClass("Name", "Address", age),
                         // many more
                     );

Note: this will create a list where you can't change its size.

Answer 2

If what you want is having the cleanest and simplest initialization, you might have this :

    List<MyClass> list = MyClass.build(
        "Name", "Address", 51,  
        "a2", "c", 4,
        "v", "d", 2
    );

This uses this utility method :

public static List<MyClass> build(Object... array) {
    List<MyClass> list = new ArrayList<Test>();
    for (int i=0; i<array.length-2; i+=3) {
        list.add(new MyClass((String)array[i], (String)array[i+1], (Integer)array[i+2]));
    }
    return list;
}

Answer 3

Something like this:

List<MyClass> list = new ArrayList<MyClass>(Arrays.asList(new MyClass[] {new MyClass("Name", "Address", age}));

Of course, your class must have a constructor like this:

public MyClass(String name, String address, int age) {
...
}

Answer 4

You can use double braces initialization: -

List<MyClass> list = new ArrayList<MyClass>() {
    {
        add(new MyClass("name", "address", 23));
        add(new MyClass("name2", "address2", 45));
    }
};

As you can see that, inner braces is just like an initializer block, which is used to initialize the list in one go..

Also note the semi-colon at the end of your double-braces

Answer 5

The "best" way to do this in an effective way would be to :

List<MyClass> list = new ArrayList<MyClass>();

 list.add(new MyClass("name", "address", 23));
 list.add(new MyClass("name2", "address2", 45));

although it requires a lot of typing but as you can clearly see this is more efficient

Another alternative would be to use google guava (not tested for efficiency):

ArrayList<MyClass> list = new ArrayList<MyClass>(
           new MyClass("name", "address", 23), 
           new MyClass("name2", "address2", 45) );

The required import is import static com.google.common.collect.Lists.newArrayList;

also, you can use double braces initialization as originally proposed by @Rohit Jain: -

List<MyClass> list = new ArrayList<MyClass>() {
    {
        add(new MyClass("name", "address", 23));
        add(new MyClass("name2", "address2", 45));
    }
};

As you can see that, inner braces is just like an initializer block, which is used to initialize the list in one go..

note the semi-colon at the end of your double-braces

also note the last method has some downsides as discussed here.

Answer 6

You can instantiate ArrayList like so:

new ArrayList<myclass>() {{
  add(new MyClass("Name", "Address", age));
}};

This creates an anonymous inner class that actually extends ArrayList, with an initialiser block that calls add. This is obviously completely filthy and will make your colleagues want to hurt you, so you should use Arrays.asList instead. :)