//氣泡排序法
        int a[]={23,34,12,21};
        int temp;
        //Arrays.sort(a);
        for (int f = 0; f < a.length; f++) {
            for (int i = 0; i < a.length-f-1; i++) {
                if(a[i]>a[i+1]){
                    temp=a[i+1];
                    a[i+1]=a[i];
                    a[i]=temp;
                }
            }
        }
        for
 
 (int i = 0; i < a.length; i++) {
            System.out.println(a[i]);
        }

    //求平均數
    float a;
    int[] array=new int [5];
    int i = 0;
    float sum=0;
    for (; i < array.length; i++) {
        Scanner sca=new Scanner(System.in);
        array[i]=sca.nextInt();

        sum+=array[i];
    }


    a=sum/5;
    System.out.println(a);
 

        //把字串中的大寫換成小寫，小寫換成大寫
        String s="abc1ffFFJJKLOl";
        String s1 = "";
        for (int i = 0; i < s.length(); i++) {
            char a=s.charAt(i);//得到字串中的字元
            //判斷大小寫
            if(a>='a'&&a<='z'){
                a=(char) (a-32);    
            }else if
 
(a>='A'&&a<='Z'){
                a=(char)(a+32); 
            }
            //把字元造型成字串
            s1=s1.concat(""+a);
        }
        System.out.println(s1);




或
        //將字串中的大寫變小寫，小寫變大寫
        String s1 = new String ("AccHujR55");
        //String s1 = "AccHujR55";
        String s4 = "";
        for (int j = 0; j < s1.length(); j++) {
            char c = s1.charAt(j);
            if (c>='a'&&c<='z'){
                c = Character.toUpperCase(c);
            }else if (c>='A'&&c<='Z'){
                c = Character.toLowerCase(c);
            }
            s4=s4.concat(""+c);
        }

        System.out.println(s4);

import java.util.Scanner;

public class Buffer {
    //一串整數，從左開始每個三個插入一個逗號
    //String類的字串是不可以更改的，StringBuffer類的字串是可以更改的
    public static void main(String[] args) {
        // TODO Auto-generated method stub

        StringBuffer buffer=new StringBuffer("123456789");

        for (int i = 3; i < buffer.length(); i+=4) {
            buffer.insert(i,',');

        }
        System.out.println(buffer);


    }

}