/**
     * 求我們1-n的和
     * 函數(shù)名字必須采用小駝峰
     * @param n 輸入一個數(shù)字
     */
    public static int sumAdd(int n){
        int sum = 0;
        for(int i = 1;i <= 10;i++){
            sum += i;
        }
        return sum;
    }
 
    public static void main(String[] args) {
        int ret = sumAdd(10);//方法的調(diào)用
    }

    /**
     * 求我們1-n的和
     * 函數(shù)名字必須采用小駝峰
     * @param n 輸入一個數(shù)字
     */
    public static int sumAdd(int n){
        int sum = 0;
        for(int i = 1;i <= 10;i++){
            sum += i;
        }
        return sum;
    }
 
    public static void main(String[] args) {
        int ret = sumAdd(10);//方法的調(diào)用
        System.out.println(sumAdd(10)*2);//函數(shù)的返回值，支持鏈式調(diào)用
    }

用函數(shù)的方法求n的階乘之和
public static int Fac(int n) {
        int sum = 1;
        for (int i = 1; i <= n; i++) {
            sum = sum * i;
        }
        return sum;
    }
    /**
     * 求n的階乘之和
     * @param
     */
    public static int facSum(int n){
        int ret = 0;
        for (int i = 1;i <= n; i++){
            ret = ret + Fac(i);
        }
        return ret;
    }
 
    public static void main(String[] args) {
 
        System.out.println(facSum(5));
    }
}

1.Java無法通過傳地址的方式交換兩個值的變量，后續(xù)會講怎么做
public class TestDemo {
    public static void swap(int a,int b){//交換兩個變量的值
        int tmp = a;
        a = b;
        b = tmp;
    }
 
    public static void main(String[] args) {
        int a = 10;
        int b = 10;
        System.out.println("交換實參前:"+a+" " +b);
        swap(&a,b);//Java是做不到取地址的，如果想要寫一個函數(shù)交換兩個數(shù)的的值，只能把a和b的值放到堆上
        System.out.println("交換實參后:"+a+" " +b);
 
    }
}

   public static void login(){
        int count = 3;
        Scanner scanner = new Scanner(System.in);
        while(count != 0){
            System.out.println("請輸入你的密碼");
            String password = scanner.nextLine();
            if(password.equals("123456")){//equals的返回值是true或者false
                System.out.println("登錄成功了");
                break;
            }else{
                count--;
                System.out.println("你輸錯密碼了，你還有"+count+"次機會");
 
            }
        }
 
    }
 
    public static void main(String[] args) {
        login();
 
    }

 求水仙花數(shù)   
public static void findNum(int n){
 
        for (int i = 1; i <=n; i++) {
            int count = 0;//數(shù)字的位數(shù)
            int tmp = i;
            while(tmp != 0){
                count++;
                tmp = tmp/10;
            }
            tmp = i;
            int sum = 0;
            while(tmp != 0){
                sum += Math.pow(tmp%10,count);
                tmp/=10;
            }
            if(sum == i){
                System.out.println(i);
            }
 
        }
 
    }
 
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int n = scanner.nextInt();
        findNum(n);
 
    }

調(diào)整數(shù)組順序使得奇數(shù)位于偶數(shù)之前，調(diào)整之后，不關(guān)心大小順序
public class TestDemo {
 
 
    public static void main(String[] args) {
        int[]arr = {1,2,3,4,5,6,7,8,9};
        int left = 0;
        int right = arr.length-1;
        while(left < right){
            while(left < right && arr[left] % 2 != 0){
                left++;
            }
            while(left < right && arr[right] % 2== 0){
                right--;
            }
            int tmp = arr[left];
            arr[left] = arr[right];
            arr[right] = tmp;
        }
        for (int i = 0; i <arr.length ; i++) {
            System.out.print(arr[i]+" ");
 
        }
 
    }

}

1.用函數(shù)求三個數(shù)的最大值
public class TestDemo {
 
 
 
    public static int Max(int a,int b){
        return a > b? a : b;
 
    }
        public static int Max1(int a,int b,int c){
        return Max(Max(a,b),c);
        }
 
    public static void main(String[] args) {
        System.out.println(Max1(4, 6, 8));
 
    }
 
}