第五章：数组与集合

1. 性能方面优先考虑数组：
   对基本类型进行求和运算时，数组的效率是集合的10倍。
   
   
2. 对数组扩容方法：
   

   public class expandCapacity {
       public static void main(String[] args) {
           String arrays[] = new String[10];
           System.out.println(arrays.length);
           arrays = expandCapacity(arrays,13);
           System.out.println(arrays.length);
       }
       public static  <T> T[] expandCapacity(T[] datas,int newlen){
           newlen = newlen < 0 ? 0 : newlen;
           return Arrays.copyOf(datas,newlen);
       }
   }

3. 警惕数组的浅拷贝：
   

   public class shallowCopy {
       public static void main(String[] args) {
           int balloonNum=7;
           Balloon[] box = new Balloon[balloonNum];
           for (int i=0;i<balloonNum;i++){
               box[i]=new Balloon(Color.values()[i],i);
           }
           Balloon[] copybox = Arrays.copyOf(box,box.length);
           copybox[6].setColor(Color.blue);
          //打印：
           for (Balloon ballon:box){
               System.out.print(ballon.getColor()+"id:"+ballon.getId()+"  ");
           }
           System.out.println();
           System.out.println("copybox数组的值：");
           for (Balloon ballon:copybox){
               System.out.print(ballon.getColor()+"id:"+ballon.getId()+"  ");
           }
       }
       public static class Balloon{
           Color color;
           int id;
           @Override
           public String toString() {
               return "Balloon{" +
                       "color='" + color + '\'' +
                       ", id=" + id +
                       '}';
           }
           public Balloon(Color color, int id) {
               this.color = color;
               this.id = id;
           }
           public Color getColor() {
               return color;
           }
           public void setColor(Color color) {
               this.color = color;
           }
           public int getId() {
               return id;
           }
           public void setId(int id) {
               this.id = id;
           }
       }
       public static enum Color{
           Red,Orange,yellow,green,indigo,blue,violet;
       }
   }

   输出的值是：