知識延伸：ArrayList

該類也是實現(xiàn)了List的接口，實現(xiàn)了可變大小的數(shù)組，隨機訪問和遍歷元素時，提供更好的性能。該類也是非同步的,在多線程的情況下不要使用。ArrayList 增長當(dāng)前長度的50%，插入刪除效率低。

//1、創(chuàng)建一個ArrayList集合對象，在該集合中添加8種基本數(shù)據(jù)類型對應(yīng)的包裝類型，。通過循環(huán)遍歷打印出所有對象。

package a;

import java.util.ArrayList;

import java.util.Iterator;

public class jihe {

public static void main(String[] argss) {

ArrayList s = new ArrayList();

Byte A1 = 5;

Integer A2 = 20;

Float A4 = (float) 1314;

Long A3 = (long) 9.9;

Character A5 = 'a';

String A6 = "anan";

Boolean A7 = true;

Double A8 = 520.0;

s.add(A8);

s.add(A7);

s.add(A6);

s.add(A5);

s.add(A4);

s.add(A3);

s.add(A1);

for (int i=0; i<s.size(); i++) {

System.out.println(s.get(i));

}

}

}

// 2、創(chuàng)建一個ArrayList集合對象，創(chuàng)建五個不同的對象Apple, Banana,將這些對象放入集合中，并通

// 過循環(huán)遍歷打印出來。

package a;

import java.util.ArrayList;

import java.util.Iterator;

public class jihe {

public static void main(String[] args) {

ArrayList s = new ArrayList();

shangping A1 = new shangping("Apple");

shangping A2 = new shangping("Banana");

shangping A3 = new shangping("AK47");

shangping A4 = new shangping("AWM");

shangping A5 = new shangping("98k");

s.add(A1);

s.add(A2);

s.add(A3);

s.add(A4);

s.add(A5);

for (int i = 0; i < s.size(); i++) {

System.out.println(s.get(i).toString());

}

}

}class shangping{

String name ;

public shangping(String name){

// TODO Auto-generated constructor stub

this.name=name;

}

@Override

public String toString() {

return "商品名:" + name;

}

}

//3、創(chuàng)建一個只能存放Apple的ArrayList，通過循環(huán)添加6個Apple對象。然后通過循環(huán)遍歷打印出來

package a;

import java.util.ArrayList;

import java.util.Iterator;

public class jihe {

public static void main(String[] args) {

ArrayList<Apple> s = new ArrayList();

for (int i = 0; i < 6; i++) {

s.add(new Apple(i));

}

for (int i =0; i <s.size(); i++) {

System.out.println(s.get(i).ID);

}

}

}

class Apple {

int ID;

public Apple(int ID) {

// TODO Auto-generated corr'structor stub

this.ID = ID;

}

public int getID() {

return ID;

}

}

// 1.創(chuàng)建一個學(xué)生類，包含學(xué)生編號，姓名，性別，成績，將學(xué)生放入類集合中，添加5名學(xué)生，算出學(xué)生的平均成績

package a;

import java. util. ArrayList;

import java. util. Iterator ;

public class jihe{

public static void main(String[] arrgs) {

ArrayList s=new ArrayList();

Studic A1=new Studic("5_20", "詩名",'男',95);

Studic A2=new Studic("1_31", "書名",'男',92);

Studic A3=new Studic("4_52", "畫名",'男',90);

Studic A4=new Studic("2_22", "唱名",'男',111);

Studic A5=new Studic("6_66", "帥名",'男',134);

s. add(A1) ;

s. add(A2) ;

s. add(A3) ;

s. add(A4) ;?

s. add(A5) ;

double sum=0;

for(int i=0;i<s.size();i++) {

Studic k=(Studic)s.get(i) ;?

sum+=k.zj;}

System. out. println("學(xué)生的平均成績:"+sum/s.size());

}}

class Studic{

String ID;

String name;

char sex ;

double zj;

public Studic (String ID, String name, char sex, double zj) {

this. ID=ID;

this. name=name ;

this. sex=sex;

this. zj=zj;

}

}

// 2.在第一題的基礎(chǔ)上，讓用戶輸入學(xué)生編號，修改學(xué)生的成績

package a;

import java. util. ArrayList;

import java. util.Iterator ;

import java. util. Scanner;

public class jihe{

public static void main(String[] args) {

ArrayList s=new ArrayList() ;

Studic A1=new Studic("5_20", "詩名",'男',95);

Studic A2=new Studic("1_31", "書名",'男',92);

Studic A3=new Studic("4_52", "畫名",'男',90);

Studic A4=new Studic("2_22", "唱名",'男',111);

Studic A5=new Studic("6_66", "帥名",'男',134);

s. add(A1) ;

s. add(A2) ;

s. add(A3) ;

s. add (A4);

s. add(A5) ;

for(int i=0;i<s. size() ;i++) {

System. out. println(s.get(i).toString());}

Scanner sc=new Scanner (System. in);

System. out.println("請輸入學(xué)生編號");

String bh=sc.next();

System.out.println("請輸入修改的成績");

double xg=sc.nextDouble() ;

for(int i=0;i<s.size();i++){

Studic k= (Studic)s.get(i) ;

if(k. ID. equals (bh)) {

k. zj=xg;

}

}

double sum=0;

for(int i=0;i<s.size();i++) {

Studic k=(Studic)s.get(i) ;?

sum+=k.zj;}

System. out. println("學(xué)生的平均成績:"+sum/s.size());

}}

class Studic{

String ID;

String name;

char sex;

double zj;

public Studic(String ID, String name, char sex, double zj) {

// TODO Auto-generated constructor stub

this. ID=ID;

this. name=name ;

this. sex=sex;

this. zj=zj;

}

@Override

public String toString() {return"編號:"+ ID + "\t名字:"+ name +"\t性別:"+ sex + "\t成績:"+ zj;

? }

}