java面试题总结（一）

1、写一个标准的单例模式

public class Singleton {

    private static Singleton singleton;

    static{

      singleton=new Singleton();

    }

    private Singleton(){}

    public static Singleton getInstance(){

      return singleton;

    }

}

2、排序一个数组 [F,a,f,h,A,g,K],要求输出[A,a,F,f,g,h,K]

答：

核心代码：

Collections.sort(list, String.CASE_INSENSITIVE_ORDER);//根据指定的字母方式排序

package lp;

import java.text.SimpleDateFormat;

import java.util.*;

public class ListTest {

public static void main(String [] args ){

   //String[] strArray = new String[] {"z", "a", "C"};

        // List list = Arrays.asList(strArray);

        // Collections.sort(list);//根据元素自然顺序排序

        // Collections.sort(list, String.CASE_INSENSITIVE_ORDER);//根据指定的字母方式排序   

       //   Collections.sort(list, Collections.reverseOrder());//根据反转自然顺序方式排序

       //   Collections.reverse(list);//反转列表排序

       }

}

*****************************************

public class Test_Array{

              public static char[] sort(char[] c){

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

                       for(int j=i;j<c.length;j++){

                                  if(c[i]>='A'&&c[i]<='Z'){

                                         if((c[j]>='A'&&c[j]<='Z'&&c[i]>c[j])||(c[j]>='a'&&c[j]<='z'&&c[i]+32>c[j])){

                                                char temp = c[j];

                                                c[j] = c[i];

                                                c[i] = temp;

                                         }

                                  }else if(c[i]<='a'&&c[i]>='z'){

                                         if((c[j]>='a'&&c[j]<='z'&&c[i]>c[j])||(c[j]>='A'&&c[j]<='Z'&&c[i]-32>=c[j])){

                                                char temp = c[j];

                                                c[j] = c[i];

                                                c[i] = temp;

                                         }

                                   }

                       }

                     } 

              }

              public void show(char[] d){

                     for(char u:d){

                            System.out.println(u);

                     }

              }

              public static void main(String[] args){

                     String str = "FafhAgK";

                     char[] c = str.toCharArray();

                     char[] d = Test_Array.sort(c);

                     Test_Array.show(d);

              }

   }

   ***********************************

 

3、写一个通用的查询语句,连接Orcle数据库的,用prepareStatement

public void testJdbc(){

Connection con = null;

PreparedStatement ps = null;

ResultSet rs = null;

try{

//step1：注册驱动；

Class.forName("oracle.jdbc.driver.OracleDriver");

//step 2：获取数据库连接；

con=DriverManager.getConnection(

"jdbc:oracle:thin:@192.168.0.39:1521:tarena","openlab","open123");

/************************查询************************/

//step 3：创建Statement；

String sql = "SELECT id, fname, lname, age, FROM

Person_test";

ps = con.prepareStatement(sql);

//step 4 ：执行查询语句，获取结果集；

rs = ps.executeQuery();

//step 5：处理结果集—输出结果集中保存的查询结果；

while (rs.next()){

System.out.print("id = " + rs.getLong("id"));

System.out.print(" , fname = " +rs.getString("fname"));

System.out.print(" , lname = " +rs.getString("lname"));

System.out.print(" , age = " + rs.getInt("age"));

}

/************************JDBC 修改*********************/

sql = "UPDATE Person_Tbl SET age=23 WHERE id = ?";

ps = con.prepareStatement(sql);

ps.setLong(1, 88);

int rows = ps.executeUpdate();

System.out.println(rows + " rows affected.");

} catch (Exception e){

e.printStackTrace();

} finally{

try{

con.close(); //关闭数据库连接，以释放资源。

} catch (Exception e1) {

}

}

}