admin 管理员组文章数量: 1086794
Java集合框架学习（五） ArrayList详解
Arraylist介绍
Arraylist类实现了List接口。
public class ArrayList<E>
extends AbstractList<E>
implements List<E>, RandomAccess, Cloneable, Serializable因为其功能性和灵活性而被广泛使用。
绝大多数开发者选择ArrayList来替代Array，因为其很好的伸缩性。
因为数组的长度是固定的，并且在删除元素后其所占空间并不会回收。
而ArrayList则相反，长度是随元素大小动态收缩的。
入门例子
package com.dylan.collection;import java.util.ArrayList;/*** @author xusucheng* @create 2018-01-28**/
public class ArrayListExample {public static void main(String args[]) {/*Creation of ArrayList: I'm going to add String*elements so I made it of string type */ArrayList<String> obj = new ArrayList<String>();/*This is how elements should be added to the array list*/obj.add("Ajeet");obj.add("Harry");obj.add("Chaitanya");obj.add("Steve");obj.add("Anuj");/* Displaying array list elements */System.out.println("Currently the array list has following elements:"+obj);/*Add element at the given index*/obj.add(0, "Rahul");obj.add(1, "Justin");/*Remove elements from array list like this*/obj.remove("Chaitanya");obj.remove("Harry");System.out.println("Current array list is:"+obj);/*Remove element from the given index*/obj.remove(1);System.out.println("Current array list is:"+obj);}
}
Currently the array list has following elements:[Ajeet, Harry, Chaitanya, Steve, Anuj]
Current array list is:[Rahul, Justin, Ajeet, Steve, Anuj]
Current array list is:[Rahul, Ajeet, Steve, Anuj]
Arraylist常用方法
1) add( Object o): 添加元素obj.add("hello");2) add(int index, Object o): 在指定位置添加元素，位置从0开始计算obj.add(2, "bye");3) remove(Object o): 删除元素obj.remove("Chaitanya");4) remove(int index): 删除指定位置上的元素obj.remove(3);5) set(int index, Object o): 使用指定元素替代指定位置上的元素obj.set(2, "Tom");6) int indexOf(Object o): 找到指定元素的位置（下标），找不到返回-1int pos = obj.indexOf("Tom");7) Object get(int index): 返回指定位置上的元素String str= obj.get(2);8) int size(): 获得ArrayList的大小，即元素的个数int numberofitems = obj.size();9) boolean contains(Object o): 判断是否包含指定元素，包含返回true，不包含返回falseobj.contains("Steve");10) clear(): 清空ArrayList，即删除其中所有元素obj.clear();初始化ArrayList方法
1.使用Arrays.asList
ArrayList<Type> obj = new ArrayList<Type>(Arrays.asList(Object o1, Object o2, Object o3, ....so on));package com.dylan.collection;import java.util.ArrayList;
import java.util.Arrays;/*** @author xusucheng* @create 2018-01-28**/
public class InitializeArrayListExample1 {public static void main(String args[]) {ArrayList<String> obj = new ArrayList<String>(Arrays.asList("Pratap", "Peter", "Harsh"));System.out.println("Elements are:"+obj);}
}
2.使用匿名内部类
ArrayList<T> obj = new ArrayList<T>(){{add(Object o1);add(Object o2);add(Object o3);......}};package com.dylan.collection;import java.util.ArrayList;
import java.util.Arrays;/*** @author xusucheng* @create 2018-01-28**/
public class InitializeArrayListExample2 {public static void main(String args[]) {ArrayList<String> cities = new ArrayList<String>(){{add("Delhi");add("Agra");add("Chennai");}};System.out.println("Content of Array list cities:"+cities);}
}
3.正常方式
ArrayList<T> obj = new ArrayList<T>();obj.add("Object o1");obj.add("Object o2");obj.add("Object o3");......package com.dylan.collection;import java.util.ArrayList;/*** @author xusucheng* @create 2018-01-28**/
public class InitializeArrayListExample3 {public static void main(String args[]) {ArrayList<String> books = new ArrayList<String>();books.add("Java Book1");books.add("Java Book2");books.add("Java Book3");System.out.println("Books stored in array list are: "+books);}
}
4.使用Collections.nocopies
ArrayList<T> obj = new ArrayList<T>(Collections.nCopies(count, element));package com.dylan.collection;import java.util.ArrayList;
import java.util.Collections;/*** @author xusucheng* @create 2018-01-28**/
public class InitializeArrayListExample4 {public static void main(String args[]) {ArrayList<Integer> intlist = new ArrayList<Integer>(Collections.nCopies(10, 5));System.out.println("ArrayList items: "+intlist);}
}
遍历ArrayList方法
1.For Loop
2.Advanced for loop
3.While Loop
4.Iterator
5.Enumeration
package com.dylan.collection;import java.util.ArrayList;
import java.util.Collections;
import java.util.Enumeration;
import java.util.Iterator;/*** @author xusucheng* @create 2018-01-28**/
public class LoopArrayListExample {public static void main(String[] args) {ArrayList<String> arrayList = new ArrayList<String>();arrayList.add("Jack");arrayList.add("Tom");arrayList.add("Lucy");arrayList.add("Brant");/* For Loop for iterating ArrayList */System.out.println("For Loop");for (int counter = 0; counter < arrayList.size(); counter++) {System.out.println(arrayList.get(counter));}/* Advanced For Loop*/System.out.println("Advanced For Loop");for (String str : arrayList) {System.out.println(str);}/* While Loop for iterating ArrayList*/System.out.println("While Loop");int count = 0;while (arrayList.size() > count) {System.out.println(arrayList.get(count));count++;}/*Looping Array List using Iterator*/System.out.println("Iterator");Iterator iter = arrayList.iterator();while (iter.hasNext()) {System.out.println(iter.next());}/*using Enumeration*/// Get the Enumeration objectEnumeration<String> e = Collections.enumeration(arrayList);// Enumerate through the ArrayList elementsSystem.out.println("Enumeration: ");while(e.hasMoreElements()){System.out.println(e.nextElement());}}}
其他常见操作
1.ArrayList排序
1）升序
2）降序Collections.sort(arrayList);
Collections.sort(arrayList, Collections.reverseOrder());
或
Collections.sort(arrayList);
Collections.reverse(arrayList);3）排序对象ArrayList
package com.dylan.collection;import java.util.Comparator;/*** @author xusucheng* @create 2018-01-28**/
public class Student implements Comparable<Student> {private String studentname;private int rollno;private int studentage;public String getStudentname() {return studentname;}public void setStudentname(String studentname) {this.studentname = studentname;}public int getStudentage() {return studentage;}public void setStudentage(int studentage) {this.studentage = studentage;}public int getRollno() {return rollno;}public void setRollno(int rollno) {this.rollno = rollno;}public Student(int rollno, String studentname, int studentage) {this.rollno = rollno;this.studentname = studentname;this.studentage = studentage;}@Overridepublic String toString() {return "[ rollno=" + rollno + ", name=" + studentname + ", age=" + studentage + "]";}@Overridepublic int compareTo(Student comparestu) {int compareage=((Student)comparestu).getStudentage();/* For Ascending order*/return this.studentage-compareage;}
}
package com.dylan.collection;import java.util.ArrayList;
import java.util.Collections;/*** @author xusucheng* @create 2018-01-28**/
public class ArrayListSorting {public static void main(String args[]){ArrayList<Student> arraylist = new ArrayList<Student>();arraylist.add(new Student(223, "Chaitanya", 26));arraylist.add(new Student(245, "Rahul", 24));arraylist.add(new Student(209, "Ajeet", 32));Collections.sort(arraylist);for(Student str: arraylist){System.out.println(str);}}
}
[ rollno=245, name=Rahul, age=24]
[ rollno=223, name=Chaitanya, age=26]
[ rollno=209, name=Ajeet, age=32]
如果需要更高级的比较策略，请使用：Comparator
import java.util.Comparator;
public class Student {private String studentname;private int rollno;private int studentage;public Student(int rollno, String studentname, int studentage) {this.rollno = rollno;this.studentname = studentname;this.studentage = studentage;}...//Getter and setter methods same as the above examples.../*Comparator for sorting the list by Student Name*/public static Comparator<Student> StuNameComparator = new Comparator<Student>() {public int compare(Student s1, Student s2) {String StudentName1 = s1.getStudentname().toUpperCase();String StudentName2 = s2.getStudentname().toUpperCase();//ascending orderreturn StudentName1pareTo(StudentName2);//descending order//return StudentName2pareTo(StudentName1);}};/*Comparator for sorting the list by roll no*/public static Comparator<Student> StuRollno = new Comparator<Student>() {public int compare(Student s1, Student s2) {int rollno1 = s1.getRollno();int rollno2 = s2.getRollno();/*For ascending order*/return rollno1-rollno2;/*For descending order*///rollno2-rollno1;}};@Overridepublic String toString() {return "[ rollno=" + rollno + ", name=" + studentname + ", age=" + studentage + "]";}}import java.util.*;
public class Details {public static void main(String args[]){ArrayList<Student> arraylist = new ArrayList<Student>();arraylist.add(new Student(101, "Zues", 26));arraylist.add(new Student(505, "Abey", 24));arraylist.add(new Student(809, "Vignesh", 32));/*Sorting based on Student Name*/System.out.println("Student Name Sorting:");Collections.sort(arraylist, Student.StuNameComparator);for(Student str: arraylist){System.out.println(str);}/* Sorting on Rollno property*/System.out.println("RollNum Sorting:");Collections.sort(arraylist, Student.StuRollno);for(Student str: arraylist){System.out.println(str);}}
}Student Name Sorting:
[ rollno=505, name=Abey, age=24]
[ rollno=809, name=Vignesh, age=32]
[ rollno=101, name=Zues, age=26]
RollNum Sorting:
[ rollno=101, name=Zues, age=26]
[ rollno=505, name=Abey, age=24]
[ rollno=809, name=Vignesh, age=32]
2.将一个ArrayList所有元素插入到另一个ArrayList中（addAll）
import java.util.ArrayList;
public class ExampleOfaddAll {public static void main(String[] args) { // ArrayList1 of String typeArrayList<String> al = new ArrayList<String>();al.add("Hi");al.add("hello");al.add("String");al.add("Test");System.out.println("ArrayList1 before addAll:"+al);//ArrayList2 of String TypeArrayList<String> al2 = new ArrayList<String>();al2.add("Text1");al2.add("Text2");al2.add("Text3");al2.add("Text4");//Adding ArrayList2 into ArrayList1al.addAll(al2);System.out.println("ArrayList1 after addAll:"+al);}
}或是插入到指定位置：
import java.util.ArrayList;
public class ExampleOfaddAllMethod {public static void main(String[] args) {// ArrayList1 ArrayList<String> al = new ArrayList<String>();al.add("Apple");al.add("Orange");al.add("Grapes");al.add("Mango");System.out.println("ArrayList1 before addAll:"+al);//ArrayList2 ArrayList<String> al2 = new ArrayList<String>();al2.add("Fig");al2.add("Pear");al2.add("Banana");al2.add("Guava");System.out.println("ArrayList2 content:"+al2);//Adding ArrayList2 in ArrayList1 at 3rd position(index =2)al.addAll(2, al2);System.out.println("ArrayList1 after adding ArrayList2 at 3rd Pos:\n"+al);}
}3.获取ArrayList子集（subList）
使用：
List subList(int fromIndex, int toIndex)import java.util.ArrayList;
import java.util.List;
public class SublistExample {public static void main(String a[]){ArrayList<String> al = new ArrayList<String>();//Addition of elements in ArrayListal.add("Steve");al.add("Justin");al.add("Ajeet");al.add("John");al.add("Arnold");al.add("Chaitanya");System.out.println("Original ArrayList Content: "+al);//Sublist to ArrayListArrayList<String> al2 = new ArrayList<String>(al.subList(1, 4));System.out.println("SubList stored in ArrayList: "+al2);//Sublist to ListList<String> list = al.subList(1, 4);System.out.println("SubList stored in List: "+list);}
}Original ArrayList Content: [Steve, Justin, Ajeet, John, Arnold, Chaitanya]
SubList stored in ArrayList: [Justin, Ajeet, John]
SubList stored in List: [Justin, Ajeet, John]
4.同样是清空操作，clear性能好于removeAll
5.比较2个ArrayList
import java.util.ArrayList;
public class Details
{public static void main(String [] args){ArrayList<String> al1= new ArrayList<String>();al1.add("hi");al1.add("How are you");al1.add("Good Morning");al1.add("bye");al1.add("Good night");ArrayList<String> al2= new ArrayList<String>();al2.add("Howdy");al2.add("Good Evening");al2.add("bye");al2.add("Good night");//Storing the comparison output in ArrayList<String>ArrayList<String> al3= new ArrayList<String>();for (String temp : al1)al3.add(al2.contains(temp) ? "Yes" : "No");System.out.println(al3);//Storing the comparison output in ArrayList<Integer>ArrayList<Integer> al4= new ArrayList<Integer>();for (String temp2 : al1)al4.add(al2.contains(temp2) ? 1 : 0);System.out.println(al4);}
}[0, 0, 0, 1, 1]
6.克隆一个ArrayList
import java.util.ArrayList;
public class Details {public static void main(String a[]){ArrayList<String> al = new ArrayList<String>();//Adding elements to the ArrayListal.add("Apple");al.add("Orange");al.add("Mango");al.add("Grapes");System.out.println("ArrayList: "+al);ArrayList<String> al2 = (ArrayList<String>)al.clone();System.out.println("Shallow copy of ArrayList: "+ al2);//add and remove on original ArrayListal.add("Fig");al.remove("Orange");//Display of both ArrayLists after add & removeSystem.out.println("Original ArrayList:"+al);System.out.println("Cloned ArrayList:"+al2);}
}7.将ArrayList转换为数组
方法1：手工方式
import java.util.*;public class ArrayListTOArray {public static void main(String[] args) {/*ArrayList declaration and initialization*/ArrayList<String> arrlist= new ArrayList<String>();arrlist.add("String1");arrlist.add("String2");arrlist.add("String3");arrlist.add("String4");/*ArrayList to Array Conversion */String array[] = new String[arrlist.size()]; for(int j =0;j<arrlist.size();j++){array[j] = arrlist.get(j);}/*Displaying Array elements*/for(String k: array){System.out.println(k);}}
}方法2：使用toArray方法
import java.util.*;public class Example {public static void main(String[] args) {/*ArrayList declaration and initialization*/ArrayList<String> friendsnames= new ArrayList<String>();friendsnames.add("Ankur");friendsnames.add("Ajeet");friendsnames.add("Harsh");friendsnames.add("John");/*ArrayList to Array Conversion */String frnames[]=friendsnames.toArray(new String[friendsnames.size()]);/*Displaying Array elements*/for(String k: frnames){System.out.println(k);}}
}8.将数组转换为ArrayList
方法1：手工方式
import java.util.*;public class Details {public static void main(String[] args) {/*ArrayList declaration*/ArrayList<String> arraylist= new ArrayList<String>();/*Initialized Array*/String array[] = {"Text1","Text2","Text3","Text4"}; /*array.length returns the current number of * elements present in array*/for(int i =0;i<array.length;i++){/* We are adding each array's element to the ArrayList*/arraylist.add(array[i]);}/*ArrayList content*/for(String str: arraylist){System.out.println(str);}}
}方法2：Arrays.asList()
import java.util.*;public class ArrayToArrayList {public static void main(String[] args) {/* Array Declaration and initialization*/String citynames[]={"Agra", "Mysore", "Chandigarh", "Bhopal"};/*Array to ArrayList conversion*/ArrayList<String> citylist= new ArrayList<String>(Arrays.asList(citynames));/*Adding new elements to the converted List*/citylist.add("New City2");citylist.add("New City3");/*Final ArrayList content display using for*/for (String str: citylist){System.out.println(str);}}
}方法3：Collections.addAll
import java.util.*;public class Example2 {public static void main(String[] args) {/* Array Declaration and initialization*/String array[]={"Hi", "Hello", "Howdy", "Bye"};/*ArrayList declaration*/ArrayList<String> arraylist= new ArrayList<String>();/*Conversion*/Collections.addAll(arraylist, array);/*Adding new elements to the converted List*/arraylist.add("String1");arraylist.add("String2");/*Display array list*/for (String str: arraylist){System.out.println(str);}}
}ArrayList和Vector对比
1.不同点
1) 线程同步: ArrayList 是非线程同步的，Vector 是线程同步的
2) 调整大小: 虽然两者大小都是动态分配的，但分配方式不同
ArrayList 每次增加一半大小
Vector 每次增加2倍
3) 性能: ArrayList 因为是非线程安全所以性能很好，
Vector 由于在操作中需要加锁以阻塞其他线程修改，所以性能比较差。
4) 快速失败:
首先，什么是快速失败？
如果一个集合（ArrayList, Vector等）在其创建了迭代器后又被修改，将抛出ConcurrentModificationException。
举个例子：
ArrayList<String> arrayList = new ArrayList<String>();arrayList.add("Jack");arrayList.add("Tom");arrayList.add("Lucy");arrayList.add("Brant");/*Looping Array List using Iterator*/System.out.println("Iterator");Iterator iter = arrayList.iterator();//remove one elementarrayList.remove(0);while (iter.hasNext()) {System.out.println(iter.next());}Iterator
Exception in thread "main" java.util.ConcurrentModificationExceptionat java.util.ArrayList$Itr.checkForComodification(ArrayList.java:901)at java.util.ArrayList$Itr.next(ArrayList.java:851)at com.dylan.collection.LoopArrayListExample.main(LoopArrayListExample.java:28)at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)at java.lang.reflect.Method.invoke(Method.java:498)at com.intellij.rt.execution.application.AppMain.main(AppMain.java:140)
在你删除元素后，迭代器迭代的时候就抛异常了！
在这一点上,Vector创建的Enumeration迭代不是快速失败的。
2.相同点
1）内部都使用数组数据结构
2）两者返回的迭代器是快速失败的
3）两者都是按元素的插入顺序来排序的
4）都允许有重复值和null值
5）空间都是动态伸缩的
3.什么时候用ArrayList和Vector？
如果你需要线程同步，使用Vector,
其他绝大多数情况都是使用ArrayList。当然,ArrayList也可以使用下面方式实现线程同步：
//Use Collecions.synzhonizedList method
List list = Collections.synchronizedList(new ArrayList());
...//If you wanna use iterator on the synchronized list, use it
//like this. It should be in synchronized block.
synchronized (list) {Iterator iterator = list.iterator();while (iterator.hasNext())...iterator.next();...
}
本文标签： Java集合框架学习（五） ArrayList详解
版权声明：本文标题：Java集合框架学习（五） ArrayList详解 内容由网友自发贡献，该文观点仅代表作者本人， 转载请联系作者并注明出处：http://www.roclinux.cn/p/1700331881a400514.html， 本站仅提供信息存储空间服务，不拥有所有权，不承担相关法律责任。如发现本站有涉嫌抄袭侵权/违法违规的内容，一经查实，本站将立刻删除。
发表评论