[Java] Ch6 Sorting Array與 Enum用法

sorting array 

• public class sort {

•         public static void main(String[] args){

•                 double[] a={1.0,3.4, 8.4, 5.3, 6.9, 7.3, 2.9, 3.8};

•                 System.out.println(Arrays.toString(a));

•                 sort(a);

•                 System.out.println(Arrays.toString(a));

•         }

•         public static void sort(double[] buf){

•                 for (int i = 0;i<buf.length;i++){

•                         int smallest = indexOfSmallest(buf, i);

•                         swap(buf, i, smallest);

•                 }

•         }

• 
  

•         public static int indexOfSmallest(double[] buf, int start){

•                 int smallest = start;

•                 for(int i = start + 1; i < buf.length; i++){

•                         if(buf[smallest]> buf[i]){

•                                 smallest = i;

•                         }

•                 }

•                 return smallest;

•         }

•         public static void swap(double[] buf,int i,int j){

•                 double tmp = buf[i];

•                 buf[i] = buf[j];

•                 buf[j] = tmp;

•         }

• }

Swap 互換兩個整數

方法一：

• int x = 10, y = 20;

• System.out.printf("x = %d y = %d\n",x,y);

• int tmp = x; x = y; y = tmp;

• System.out.printf("x = %d y = %d\n",x,y);

方法二：

利用Exclusive OR運算來做Swap

•             // 利用 exclusive or 來做swap ! (此方法只限制在整數才可用)

•             int x = 1;

•             int y = 2;

•             System.out.printf("x = %d y = %d\n",x,y);

•             x ^= y; y ^= x; x ^= y;

•             System.out.printf("x = %d y = %d\n",x,y);

•                 

•             //原理說明

•             int x1,y1,x2;

•             x1 = x^y;

•             y1 = x1^y; // x^y^y 這樣等於原來的 x

•             x2 = x1^y1; // 等同於 x1^原來的 x 會等於--> 原本的 y

                

Enum

使用情境

想要做一個限制範圍內的變數

Week2.java

• public enum Week2 {

•         SUNDAY,MONDAY,TUESDAY,WEDNESDAY,THURSDAY,FRIDAY,SATURDAY

• }

Enumeration2.java

• public class Enumeration2 {

•         public static void main(String[] args){       

•                 Week2 today, someday;         

•                 today = Week2.MONDAY;

•                 someday = null;

•                 someday = Week2.valueOf("SUNDAY");

•                 System.out.println(someday);

•                 

•                 switch(today){ // switch 的後放可以放 int char byte

•                 case SATURDAY: case SUNDAY:

•                         System.out.println("today is weekend");

•                         break;

•                 default:

•                         System.out.println("today is workday");

•                 }                

•                 Week2[] allday = Week2.values();

•                 for( Week2 i:allday){

•                         System.out.println(i);

•                 }

•         }

• }

使用for each 把所有結果印出來

• Week2[] allday = Week2.values();

• for( Week2 i : allday){

•           System.out.println(i);

• }