Common operations to add, traverse, and remove collections The namespace System.Collections
ArrayList variable length array, which is used like an array Attribute Capacity Count methods Add() AddRange() Remove() RemoveAt() Clear() Contains() ToArray() A collection of Hashtable key-value pairs (KeyValuePair), similar to a dictionary
a, ArrayList operations on value types
using System;
using System.Collections;
namespace _08_ArrayList {
//ArayList Operations on value types
class Program {
static void Main( string[] args) {
//ArrayList It's not that different from an array The advantage is that unlike arrays, you don't have to specify the length The disadvantage is that the data type is unrestricted What kind of data can you put in This can lead to a lot of errors
ArrayList arylist = new ArrayList();
//ArrayList add
arylist.Add(1000);
//arylist.Add(" zhang 3");// The parameter type is object So you can add multiple types of parameters Type conversion is also required when fetching
arylist.Add(3000);
arylist.Add(4000); // Boxed operation occurs Converts a value type to a reference type
arylist.Add(5000);
int [] arr = { 1, 2, 3, 4 };
arylist.AddRange(arr); //AddRange The parameter is implemented ICollections Object of interface can 1 Sub-add array, array , ArrayList And the object that implements the interface
// The number of elements in the set use Count = An array of Length
Console .WriteLine(" Set content length " + arylist.Count);
//Capacity Is the capacity of the collection Is variable 1 a *2 growth
Console .WriteLine(arylist.Capacity);
// Access set control 1 An element
int firstlist = Convert .ToInt32(arylist[0]);
Console .WriteLine(firstlist.ToString());
//ArrayList traverse
int sum2 = 0;
for (int i = 0; i < arylist.Count; i++) {
//sum2 += Convert.ToInt32(arylist[i]);// Unpacking occurs
Console .WriteLine(arylist[i].ToString());
}
foreach (object item in arylist) {
sum2 += Convert .ToInt32(item);
}
Console .WriteLine(sum2);
//ArrayList remove Just remove the Not delete
arylist.Remove(1000); // To remove the content is 1000 the Remove Removes an internal object
arylist.RemoveAt(1); // Remove the first 2 item Remove by index
// Pay attention to Remove elements ArrayList The array will reassign the index So the best way to remove an element is to go backwards
// If I remove all the elements Direct use of Clear
//arylist.Clear();
if (arylist.Contains(3000)) {
Console .WriteLine(" contains " );
}
//ArrayList There are ToArray() But it doesn't make much sense
// This is in ArrayList Add a value type to What about reference types ???? add Student Class object?
Console .Read();
}
}
}Operations on reference types by b and ArrayList
using System;
using System.Collections;
namespace _09_ArrayListObject {
//ArrayList Operations on reference types
class Student {
public Student(string name, int age) {
this .name = name;
this .age = age;
}
private string name;
public string Name {
get {
return name;
}
set {
name = value ;
}
}
private int age;
public int Age {
get {
return age;
}
set {
age = value ;
}
}
}
class Program {
static void Main( string[] args) {
Student xyy = new Student( " Xiao yueyue " , 14);
Student fj = new Student( " feng " , 18);
Student fr = new Student( " Sister lotus " , 19);
Student xl = new Student( " Brother sharp " , 20);
ArrayList student = new ArrayList();
student.Add(xyy); // add You can also use AddRange
student.Add(fj);
student.Add(fr);
student.Add(xl);
// remove
//student.Remove(fj);// So that's the object that you're removing Not a value
//student.RemoveAt(1);// Index to remove
// Remove not to drop fj because Remove After is object Remove by index
//Student stu = new Student(" feng ", 18);
//student.Remove(stu);
//Console.WriteLine(student.Contains(stu));//false Indexed retrieval because stu with fj The address is not 1 The sample of
// traverse
for (int i = 0; i < student.Count; i++) {
Student s = student[i] as Student; // Because boxing occurs before adding so We need to unpack it now student[i] I can't point it out name the
Console .WriteLine(s.Name);
}
ArrayList ary = new ArrayList();
ary.Add( " feng " );
ary.Add( " Xiao yueyue " );
//string A class is also a reference type But there's something special here
string name = " feng " ;
Console .WriteLine(ary.Contains(name));//string The comparison is content So back true
// Student names Get student objects although ArrayList Can be implemented But it's pretty complicated And it's inefficient So let's move on HashTable
Console .Read();
}
}
}c, HashTable
using System;
using System.Collections;
namespace _10_HashTable {
class Student {
public Student(string name, int age) {
this .name = name;
this .age = age;
}
private string name;
public string Name {
get {
return name;
}
set {
name = value ;
}
}
private int age;
public int Age {
get {
return age;
}
set {
age = value ;
}
}
}
class Program {
static void Main( string[] args) {
// Still use Student Class to implement
//Hashtable Key value pair form key value Equivalent to a dictionary Can quickly find the object according to the student's name
Student xyy = new Student( " Xiao yueyue " , 14);
Student fj = new Student( " feng " , 18);
Student fr = new Student( " Sister lotus " , 19);
Student xl = new Student( " Brother sharp " , 20);
Hashtable student = new Hashtable();
student.Add( " Xiao yueyue " , xyy);
student.Add( " feng " , fj);
student.Add( " Sister lotus " , fr);
student.Add( " Brother sharp " , xl);
//student.Add(" Brother sharp ",xl);// error A key word in a dictionary key No repetition So you can't add brother sharp
// remove Because there is no index So there is no RemoveAt()
student.Remove( " Xiao yueyue " );// According to the key To remove
student.Clear();
student.ContainsKey( " feng " );// To see if it contains this bond
// traverse Because the dictionary has no index So you can't use it for To traverse Can only use foreach
// According to the key traverse Often use
foreach (object key in student.Keys) {
Student stu = student[key] as Student;
Console .WriteLine(key);
Console .WriteLine(stu.Age);
}
// According to the value traverse
foreach (object value in student.Values) {
Student stu = value as Student;
if (stu != null ) {
Console .WriteLine(stu.Age);
}
}
// If you don't press the key Don't press the value traverse To traverse the dictionary is to traverse the dictionary's key-value pairs
foreach (DictionaryEntry de in student) {
Console .WriteLine(de.Key);
Student s = de.Value as Student; // Because what you get is object type so You also need a transformation to make it usable
Console .WriteLine(s.Age);
}
Student s2 = student[" Xiao yueyue " ] as Student ;// Find the object by name Get the other properties
if (s2 != null ) {
Console .WriteLine(s2.Age);
}
Console .Read();
}
}
}d, practice
using System;
using System.Collections;
namespace _11_ArrayList practice {
class Program {
// again After understanding the problem Start writing when you have an idea code Thinking is the most important thing
static void Main( string[] args) {
// Two sets { " a " , " b " , " c " , " d " , " e " } and { " d " , " e " , " f " , " g " , " h " } , merge the two sets of removal duplicates 1 a
ArrayList ary1 = new ArrayList { "a" , "b" , "c", "d" , "e" };
ArrayList ary2 = new ArrayList { "d" , "e" , "f", "g" , "h" };
// You go through two sets
for (int i = 0; i < ary2.Count; i++) { // To iterate over ary2 Elements and ary1 Then compare If you have the same value Do not add Otherwise append to ary1 In the
if (!ary1.Contains(ary2[i])) {// There are Contains methods If there is no I don't know how complicated it is
ary1.Add(ary2[i]);
}
}
foreach (object item in ary1) {
Console .Write(item);
}
// Randomly generated 10 a 1-100 The number between ArrayList So, we want to do that 10 You can't repeat them, and they're all even
ArrayList arylist = new ArrayList();
//int numCount = 0;
while (true ) {
Random ran = new Random();
int num = ran.Next(1, 100);
if (num % 2 == 0 && !arylist.Contains(num)) { // add !arylist.Contains(num) This sentence Solve the following problems
arylist.Add(num); // Why run the general display directly 1 The number that satisfies the condition Step - by - step debugging shows the correct result??
}
if (arylist.Count == 10) {
break ;
}
}
foreach (object item in arylist) {
Console .WriteLine(item);
}
// There are 1 Two strings are separated by Spaces 1 Series of integers, write 1 A program prints out the integers by rearranging them as follows: odd on the left and even on the right. Such as' 2 7 8 3 22 9' To display the ' 7 3 9 2 8 22
string str = "2 7 8 3 22 9" ;
ArrayList ary3 = new ArrayList();
ArrayList ary4 = new ArrayList();
string [] s = str.Split(' ' );
foreach (var item in s) {
if (Convert .ToInt32(item) % 2 == 0) {
ary4.Add(item);
} else {
ary3.Add(item);
}
}
ary3.AddRange(ary4); // because ary1 A type of object So it can't be used string Of the class join Method to implement character concatenation We learned later that you can handle generic collections
string newstr = ary3[0].ToString();// Easy way to get rid of Spaces
for (int i = 1; i < ary3.Count; i++) {
newstr += " " + ary3[i];
}
Console .WriteLine(" Original string: {0} , the filtered string {1}" , str, newstr + "test" );
Console .Read();
}
}
}