JAVA Study Notes (20)-collection List, java Study Notes

JAVA Study Notes (20)-collection List, java Study Notes
ArrayList set

/** ArrayList, which implements the List interface *. When declaring an array, you must specify the element type in the array, which can be the basic data type, it can also be a reference data type * When declaring a set, you can not specify the type of its elements. The default element type is the Object type */public class Test01 {public static void main (String [] args) {// create an ArrayList set ArrayList list = new ArrayList (); // Add the element list. add ("tom"); list. add (25); list. add (1, 12.4); list. add (true); list. add (new Student (); list. add ("tom"); // features of the elements in the List set: ordered, allow repeated list. add (1, "alice"); // list. add (1, 20,250); list. Add (null); // modify the element list. set (0, "mike"); // Delete the element list. remove (1); list. remove ("tom"); list. remove (new Integer (25); // list. clear (); // clear the elements in the Set // obtain the elements in the Set/** Object obj = list. get (2); // The get () method returns an Object boolean flag = (Boolean) * obj; */boolean flag = (Boolean) list. get (2); System. out. println ("element of the SET index 2:" + flag); // you can determine whether the set includes the specified System element. out. println ("tom? "+ List. contains ("tom"); System. out. println ("whether the set is empty:" + list. isEmpty (); System. out. println ("index of mike in the Set:" + list. indexOf ("mike"); System. out. println ("number of elements:" + list. size (); // The element for (int I = 0; I <list. size (); I ++) {System. out. println (list. get (I); // get the elements in the set through the get () method} // convert the set to an array Object [] objs = list. toArray (); System. out. println ("element in the array:" + Arrays. toString (objs ));}}

ArrayList collection instance

/** ArrayList */public class Test02 {public static void main (String [] args) {// create a collection List for storing dog information = new ArrayList (); dog dog1 = new Dog ("wangcai", "Wolf Dog", 2); Dog dog2 = new Dog ("sunspot", "Labrado", 1 ); dog dog3 = new Dog ("Xiaomei", "xuenarui", 5); // Add the Dog object to the list in the collection. add (dog1); list. add (dog2); list. add (dog3); // query the number of dogs in the System. out. println ("Total" + list. size () + "dog! "); System. out. println ("respectively:"); for (Object obj: list) // use the foreach loop to traverse the set {Dog dog = (Dog) obj; // The default element type in the set is Object, which must be converted to System. out. println (dog. getName () + "," + dog. getBrand () + "," + dog. getAge () ;}}/ ** Dog class */class Dog {private String name; private String brand; private int age; public Dog (String name, String brand, int age) {super (); this. name = name; this. brand = brand; this. age = age;} public String getName () {return name;} public void setName (String name) {this. name = name;} public String getBrand () {return brand;} public void setBrand (String brand) {this. brand = brand;} public int getAge () {return age;} public void setAge (int age) {this. age = age ;}}

Vectoring set

/** Vectoring: similar to ArrayList, It is thread-safe, but its efficiency and performance are not as good as that of ArrayList, it is not recommended to use */public class Test03 {public static void main (String [] args) {// to create a Vector set Vector v = new Vector (); v. add (1, 100); v. add (new Double (6.5); v. add (new Date (); v. add ("hello"); v. add (new String ("world"); System. out. println ("number of elements:" + v. size ();/** traversal Set Method * // method 1 System. out. println ("********* method 1 ********"); for (int I = 0; I <v. size (); I ++) {System. out. println (v. get (I);} // method 2 System. out. println ("******** method 2 ********"); for (Object obj: v) {System. out. println (obj);} // method 3: Use Enumeration for iteration, applicable to Vector, HashTable, Properties, and other sets, out of date System. out. println ("********* method 3 ********"); Enumeration e = v. elements (); // call the elements () method of Vector and return an Enumeration instance while (e. hasMoreElements () {// call the hasMoreElements () method of Enumeration to determine whether the Element Object obj = e. nextElement (); // call the nextElement () method of Enumeration to obtain the current element System. out. println (obj);} // directly outputs the System set. out. println (v );}}

Stack

Import java. util. stack;/** Stack, inherited from Vector */public class Test04 {public static void main (String [] args) {// create an empty Stack stack Stack = new stack (); // inbound Stack stack. push ("tom"); stack. push ("jack"); stack. push ("alice"); // output stack System. out. println (stack. pop ());}}

Collections list set

Import java. util. using List;/** using List, which implements the List interface and linked List storage. Frequent addition, modification, or deletion has a higher validity rate */public class Test05 {public static void main (String [] args) {// create an external list set whose list = new external list (); list. add ("itany"); list. add (12); list. add (new Double (12.5); list. add (0, "Zhao Xin"); list. addFirst ("galun"); list. addLast ("cold ice"); System. out. println ("index 2 element:" + list. get (2); System. out. println ("first element:" + list. getFirst (); System. out. println ("first element:" + list. get (0); System. out. println ("last element:" + list. getLast (); System. out. println ("last element:" + list. get (list. size ()-1); System. out. println ("element in the Set:" + list); list. removeFirst (); list. removeLast (); System. out. println ("element in the Set:" + list );}}

Performance Comparison of ArrayLis, Vector, and LinkedList

Import java. util. arrayList; import java. util. using list; import java. util. vector;/** ArrayLis, Vector, and javaslist performance comparison */public class Test06 {public static void main (String [] args) {ArrayList al = new ArrayList (); vector v = new Vector (); empty list ll = new empty list (); // test ArrayList performance long time1 = System. currentTimeMillis (); // obtain the number of milliseconds before execution for (int I = 1; I <100000; I ++) {al. add (0, I);} long time2 = System. currentTimeMillis (); // obtain the number of milliseconds after execution System. out. println ("ArrayList time spent:" + (time2-time1); // test the Vector performance long time3 = System. currentTimeMillis (); for (int I = 1; I <100000; I ++) {v. add (0, I);} long time4 = System. currentTimeMillis (); System. out. println ("time spent by the Vector:" + (time4-time3); // test the duration list performance long time5 = System. currentTimeMillis (); for (int I = 1; I <100000; I ++) {ll. addFirst (I);} long time6 = System. currentTimeMillis (); System. out. println ("elapsed list time:" + (time6-time5 ));}}