[Java] BigData basis _HashSet

HashSet Profile

 HashSet data type is a collection, has the following three characteristics:

(1) may store data objects over

(2) Data can not be repeated in HashSet

(3) HashSet stored data are unordered

HashSet several common methods are as follows:

(1) add: add elements to the collection

(2) size: obtaining a set of length

(3) remove: Removes the element

(4) to traverse a set of set: a fetch iterator

Practical exercise

Special note: The following code contains acquired using an enhanced set of codes for loop element

package cn.test.logan.day06;

import java.util.ArrayList;
import java.util.HashSet;
import java.util.Iterator;

public class HashSetDemo {
    public static void main(String[] args) {
        
        // construct a HashSet object 
        HashSet <String> = hashSet new new HashSet <> ();
        
        // add data 
        hashSet.add ( "Jack" );
        hashSet.add("Jack");
        hashSet.add("Tom");
        hashSet.add("Alice");
        hashSet.add("Grace");
        
        // Get length 
        int size = hashSet.size ();
        System.out.println(size);
        
        // remove elements 
        hashSet.remove ( "Tom" );
        System.out.println(hashSet.size());
        System.out.println ( "---------------------------" );
         // iterate set collections: a fetch iterator 
        Iterator <String> Iterator = hashSet.iterator ();
         the while (iterator.hasNext ()) { // the hasNext () method is used to down "data pointer", and judges whether there is data 
            String next = iterator.next () ; //   Next () is to take the current data on the "data pointer" 
            System.out.println (Next);
        }
        System.out.println ( "---------------------------" );
         // enhanced for loop (inside the package using an iterator ) 
        for (String tmp: hashSet) {
            System.out.println(tmp);
        }
        System.out.println ( "---------------------------" );
         // array may also be used to enhance the operation for loop 
        int [ ] = ARR new new  int [] {2,4,5,6,7 };
         for ( int TMP1: ARR) {
            System.out.println(tmp1);
        }
        System.out.println ( "---------------------------" );
         // the ArrayList loop may be used for enhanced 
        ArrayList <Integer> = the arrayList new new the ArrayList <Integer> ();
        arrayList.add(10);
        arrayList.add(20);
        arrayList.add(30);
        
        for(int tmp2:arrayList) {
            System.out.println(tmp2);
        }
        
    }
}

HashSetDemo.java

 

HashSet Profile

[HashSet jiǎnjiè]

HashSet Profile