方法使用小练

Posted 2023-04-19 起名真的很难

方法的重载

public class Demo02 
    public static void main(String[] args) 
        int max = max(10,10);
        System.out.println(max);
    
    //方法的重载：方法可以重名，但是要参数类型不同
    public static double max(double num1,double num2)

        double result = 0;

        if(num1 == num2)
            System.out.println("num1==num2");
            return 0;
        

        if(num1 > num2)
            result = num1;
        else
            result = num2;
        

        return result;
    
    //比大小
    public static int max(int num1,int num2)

        int result = 0;

        if(num1 == num2)
            System.out.println("num1==num2");
            return 0;//终止方法
        

        if(num1 > num2)
            result = num1;
        else
            result = num2;
        

        return result;
    

可变参数的使用

public class Demo04 
    public static void main(String[] args) 
        Demo04 demo04 = new Demo04();
        demo04.test(1,2,3,4,5);

    

    //这样比比较麻烦，可以用可变参数
    public void method()
    public void method(int i)
    public void method(int i,int i2)
    public void method(int i,int i2,int i3)
    //可变参数
    public void test(int... i)
        System.out.println(i[0]);
        System.out.println(i[1]);
    

输出几个数的最大值

public class maxDemo 
    //输出几个数中的最大值
    public static void main(String[] args) 
        printMax(1,2,5,41,35.5);
        printMax(new double[]1,2,5,64,84);//此处不能写为new double[1,2,3,4,5],会报错
    
    public static void printMax(double...x)
        if(x.length == 0)
            System.out.println("没有输入数据");
            return ;
        
        double result =x[0];
        for(int i = 1;i<x.length;i++)//将大的值赋值给result用来返回
            if(x[i]>result)
                result = x[i];
            
        
        System.out.println("最大值为：" + result);

    

递归计算阶乘

• 尽量避免使用递归

public class Demo06 
    //计算阶乘
    public static void main(String[] args) 
        System.out.println(f(5));
    

    public static int f(int n)
        if(n == 1)
            return 1;
        else
            return n*f(n-1);
        
    

一个有问题的计算程序

• scanner.close()后，运行到scanner.nextDouble处时出现异常NoSuchElementException
• 解决办法是删除scanner.close（）语句，或者不循环

import java.util.Scanner;

public class calculatorTest 
    public static void main(String[] args) 

        while(true) 
            Scanner scanner = new Scanner(System.in);

            System.out.println("请输入第一个数");
            double a1 = scanner.nextDouble();

            System.out.println("请输入第二个数");
            double a2 = scanner.nextDouble();

            System.out.println("请输入运算符");

            String str = scanner.next();//此处用scanner.nextLine()会直接赋值为空并进入switch

                switch (str) 
                    case "+":
                        System.out.println(add(a1, a2));
                        break;
                    case "-":
                        System.out.println(subtraction(a1, a2));
                        break;
                    case "*":
                        System.out.println(multiplication(a1, a2));
                        break;
                    case "/":
                        System.out.println(division(a1, a2));
                        break;
                    default:
                        System.out.println("符号输入错误，请重新输入");
                
            scanner.close();
        

    
    public static double add(double x,double y)//定义加法
        return x+y;
    
    public static double subtraction(double x,double y)//定义减法
        return x-y;
    
    public static double multiplication(double x,double y)//定义乘法
        return x*y;
    
    public static double division(double x,double y)//定义除法
        return x/y;
    

listener 配置小练习之方法二

作业：1521 1526
环境里存在一个数据库实例A

实现：
1521监听A数据库
A数据库的信息主动注册到1526监听器上
并且通过easy connect和sqlplus sys/[email protected]网络服务名 as sysdba 方式验证

下面我想用另一种方式来实现：数据库WDD都是动态向1521  1526注册数据库
1 编辑listener.ora配置文件
LSNR2 =
  (DESCRIPTION_LIST =
    (DESCRIPTION =
      (ADDRESS = (PROTOCOL = TCP)(HOST = 172.16.195.60)(PORT = 1526))
      (ADDRESS = (PROTOCOL = TCP)(HOST = 172.16.195.60)(PORT = 1521))
    )
  )

2 编辑tnsnames.ora配置文件
LSNR2 =
  (DESCRIPTION_LIST =
    (DESCRIPTION =
      (ADDRESS = (PROTOCOL = TCP)(HOST = 172.16.195.60)(PORT = 1526))
    )
  )

3 数据库设置local_listener
alter system set local_listener=‘LSNR2‘;这里的LSNR2跟tnsnames里的名字是相同的
4 启动监听
lsnrctl start lsnr2
如果看到如下信息，证明配置正确
Listening Endpoints Summary...
  (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=172.16.195.60)(PORT=1526)))
  (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=172.16.195.60)(PORT=1521)))
Services Summary...
Service "WDDXDB.dba.oracle.com" has 1 instance(s).
  Instance "WDD", status READY, has 1 handler(s) for this service...
Service "wsweididi.dba.oracle.com" has 1 instance(s).
  Instance "WDD", status READY, has 1 handler(s) for this service...
The command completed successfully
5 客户端验证
客户端tnsnames配置文件
WDD1 =
  (DESCRIPTION =
    (ADDRESS_LIST =
      (ADDRESS = (PROTOCOL = TCP)(HOST = 172.16.195.60)(PORT = 1521))
    )
    (CONNECT_DATA =
      (SERVER = DEDICATED)
      (SERVICE_NAME = wsweididi.dba.oracle.com)
    )
  )


 
WDD2 =
  (DESCRIPTION =
    (ADDRESS_LIST =
      (ADDRESS = (PROTOCOL = TCP)(HOST = 172.16.195.60)(PORT = 1526))
    )
    (CONNECT_DATA =
      (SERVER = DEDICATED)
      (SERVICE_NAME = wsweididi.dba.oracle.com)
    )
  )
验证
1 sqlplus system/[email protected]
2 sqlplus system/[email protected]
3 sqlplus system/[email protected]:1521/wsweididi.dba.oracle.com
4 sqlplus system/[email protected]:1526/wsweididi.dba.oracle.com