day(13)The Basic Use of ArrayList<>

Collection

Collection is an interface of collection class,which defines common methods in collection(集合共有的方法)

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-|List(列表) (An Array)

Duplicate objects are allowed &It is sequential(有序的)

ArrayList

linear list structure(线性表结构)
Methods connected with 'get' are used frequently.
Pay attention to the ‘remove' method uesd in for-loop.
iterator
remove() & removeIf()
contains();
set();

class Person implements Comparable {
    protected float score;
    protected String name;
    protected int age;

    public Person(String name,float score,int age){
        this.name = name;
        this.score = score;
        this.age = age;

    }
    @Override
    public String toString() {
        return "name:"+name+ " "+"score:" + score + " "+"age:"+age;
    }

    //  Ascending order(升序)
    @Override
    public int compareTo(Person person) {
        // age can be score as well
        if(age > person.age){
            return 1;
        }else if(age == person.age){
            return  0;
        }
        return -1;
    }

    //  Descending order(降序)
    /*public int compareTo(Person person) {
        if(age > person.age){
            return -1;
        }else if(age == person.age){
            return  0;
        }
        return 1;
    }*/
}

public class MyClass {
    public static void main(String[] args) {
        //  Create an array
        //  polymorphism
        //  The Collection Object can only save one same kind of data
        List people = new ArrayList<>();
        ArrayList personList = new ArrayList<>();

        //  Add an object at the end of array
        //Person xw = new Person("小王",90,15);
        personList.add(new Person("Jack",90,15));
        personList.add(new Person("John",90,16));
        personList.add(new Person("Merry",90,17));
        //  Add data in a certain position
        personList.add(0,new Person("小王",90,14));

        //  Get one object
        Person person = personList.get(0);
        System.out.println(personList);

        // Traverse this array
        //1. for cyclic sentences
        for (int i = 0; i < personList.size(); i++){
            Person p = personList.get(i);
            // ↓ Delete the corresponding object,but this exists problems
            // ↓ And this normally won't be the method we want
            //personList.remove(i);
            //  Delete one certain object
            //personList.remove(p);
            //System.out.println(p);
        }
        System.out.println("______for-each________");

        // 2.The enhanced for-each loop(增强for循环)
        for(Person p : personList){
            //  Fail
            //personList.remove(p);
            System.out.println(p);
        }

        System.out.println("_______iterator_______");
        //  3.Ues Iterator (使用Iterator遍历器)
        // Main difference: The object will be deleted when traversed

        // Get the corresponding iterator object
        Iterator iterator = personList.iterator();
        //  Ues hasNext() to judge whether exists another one object
        //  Use next() to get the next object
       /* while(iterator.hasNext()){
            Person p = iterator.next();
            //personList.remove(p);
           iterator.remove();
        }*/
        System.out.println("*********");
        System.out.println(personList);


        System.out.println("*****removeIf******");
        //  The Delete of the Data
        //  1.Delete the data under certain condition
        //  Create a subclass object of Predicate Interface
        //MyPredicate predicate = new MyPredicate();
        //personList.removeIf(predicate);
        //System.out.println("****removeIf***");
        //System.out.println(personList);

        //  2.Use a anonymous inner class(匿名内部类)
        /*personList.removeIf(new Predicate() {
            @Override
            public boolean test(Person person) {
                if(person.age > 15){
                    // If it is true ,this object will be deleted
                    return true;
                }
                return false;
            }
        });*/


        // Sort(排序)
        // 1.The defined class by oneself should implements the Comparable Interface ↑(Person class) and override compareTo method
        //Collections.sort(personList);
        personList.sort(new Comparator() {
            @Override
            public int compare(Person person, Person t1) {
                //  Make your own rules of comparison
                return person.name.compareTo(t1.name);
            }
        });

        System.out.println(personList);

        //  Get one object
        Person person1 = personList.get(0);

        //  This is a new object.corresponding to a new person
        person = new Person("John",90,16);

        // Judge whether this object contains certain element
        if (personList.contains(person)){
            System.out.println("Here exist this person");
        }else{
            System.out.println("Here doesn't exist this person");
        }

        //  Get index of certain object
        System.out.println(personList.indexOf(person1));

        // To change the index of certain object
        personList.set(0,person1);

        // Clear all data
        personList.clear();
        System.out.println(personList);
    }

    // Create a class to implement the methods in the Predicate Interface
    //  For the 'removeIf' method
    static class MyPredicate implements Predicate {
        @Override
        public boolean test(Person person){
            if(person.age > 15 ){
                return true;
            }
            return false;
        }
    }
}

LinkList

chain list(链表结构)
Methods connected with 'add' & 'remove' methods are used fequently.

-|Set (A Collection)

Unordered(无序的)
Duplicate objects are not allowed.
HashSet method is used frequently.

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