Java Learning-Collection Interface

Keywords: Java

Collection Common Functions

Collection is the parent interface of all single-column collections, so some common methods of single-column collections (List and Set) are defined in Collection, which can be used to manipulate all single-column collections. The methods are as follows:

  • Public Boolean add (E): Adds a given object to the current collection.
  • public void clear(): Clears all elements in the collection.
  • Public Boolean remove (E): Delete a given object from the current collection.
  • Public Boolean contains (E): Determines whether a given object is included in the current collection.
  • public boolean isEmpty(): Determines whether the current collection is empty.
  • public int size(): Returns the number of elements in the collection.
  • public Object[] toArray(): Stores elements in a collection into an array.
import java.util.ArrayList;
import java.util.Collection;

public class Collection_basic {
    public static void main(String[] args) {
        Collection<String> coll = new ArrayList<>();
        System.out.println(coll); // Printed as [], indicating that soString() has been overwritten.

        /* 1. add Method
            public boolean add(E e): Add objects to geometry
            The return value is a Boolean value, which returns true successfully, but it is generally error-free and generally not accepted.
        boolean b1 = coll.add("Zhang San"); // The return value of add is that Boolean value true is add to CD-ROM migrant workers
        System.out.println("b1:" + b1);
        System.out.println(coll); // [Zhang three]

        coll.add("Li Si");
        coll.add("Wang Wu");
        coll.add("Zhao Liu");


        /* 2. remove Method
            public boolean remove(E e): Delete elements from collections
            The return value is boolean, which exists in the collection, deletes successfully, and returns true
                             The collection does not exist, deletion fails, and false is returned.
        boolean b2 = coll.remove("Zhao Liu");
        System.out.println("b2:" + b2);
        boolean b3 = coll.remove("I do not exist.");
        System.out.println("b3" + b3);


        /* 3. contains
            public boolean contains(E e): Determine whether an element is included in a collection
        boolean b4 = coll.contains("Li Si");
        System.out.println("b4:" + b4);


        /* 4. isEmpty
            public boolean isEmpty(); Set returns true for empty, not false for empty
        boolean b5 = coll.isEmpty();
        System.out.println("b5:" + b5);


        /* 5. size
            public int size(); Number of elements returned
        int s = coll.size();
        System.out.println("size:" + s);


        /* 6. toArray
            public Object[] toArray(); Store elements in a collection in an array
        Object[] arr = coll.toArray();
        for (int i = 0; i < arr.length; i++) {

        /* 7. clear
            public void clear(); Empty all elements in the collection, but do not delete the collection, and become an empty collection


Posted by rondog on Sat, 12 Oct 2019 10:31:49 -0700