构造，初始化，访问元素，添加元素，删除元素，修改元素
子类构造器
对象包装器（Integer）/数字与字符串之间的转换
package zzy;import java.util.*;import static java.lang.System.*;/** * * @author Zhu Zhengyan */public class shuzu2 { public static void main(String[] args){ ArrayList<NIUBI> a = new ArrayList<>();//定义数组a 也可 NIUBI[] b = new NIUBI[3]; b[0] = new NIUBI(1,"Bkj"); a.ensureCapacity(2); //确认容量，也可直接在上方（）中写2 a.add(new NIUBI(5,"hdasd")); a.add(new NIUBI(42,"nihaoa")); //将元素添加到数组列表中 NIUBI m = a.get(0); //获得数组列表的元素,等价于 NIUBI m = a[0]; m.show(); a.set(0,new NIUBI(2,"s")); //等价于a[0] = .... set只能替换数组中存在的元素内容，不能用于定义 NIUBI n = a.get(0); n.show(); a.add(1,new NIUBI(8,"h")); //插入一个新元素到1号位，原来的1号位及其之后的元素向后移动 NIUBI m_ = a.get(2); m_.show(); NIUBI n_ = a.get(1); n_.show(); NIUBI o_ = a.remove(1); //删除一个元素，它之后的元素都向前移动 NIUBI n__ = a.get(1); n__.show(); ArrayList<Integer> j = new ArrayList<>(5); j.add(9); int j0 = j.get(0); //out.println(j0); String s = "1"; int s_ = Integer.parseInt(s); //将数字字符串转换为数字 //out.println(s_); int x = 5; String x_ = Integer.toString(x); //将数字转换为字符串 //out.println(x_); }}class NIUBI{ private int a ; private String b ; private double c; public NIUBI(int a,String b){ this.a = a; this.b = b; } public String getString(){ return (b); } public void show(){ out.println(a+","+b); }}class niu extends NIUBI{ private char d; public niu(int a, String b,char d){ super( a, b); this.d = d; }}
