java 笔记（四）

书接上文

41.关于形参

public class Test {
	static void ParTest1(int a,char b,int[] c,char[] d,String e,String [] f) {
		a = 2;
		b = 'a';
		c[1] = 4;
		d[1] = 's';
		e = "ZXcZXcZX";
		f[1] = "adsfasd";
	} 
	public void ParTest2(int a,char b,int[] c,char[] d,String e,String [] f) {
		a = 2;
		b = 'a';
		c[1] = 4;
		d[1] = 's';
		e = "ZXcZXcZX";
		f[1] = "adsfasd";
	} 
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		int a = 1;
		char b = 'c';
		int [] c = {1,2,3};
		char [] d = {'s','h','l'};
		String str = "a string";
		String [] strarr = {"first","second","third"};
		ParTest1(a, b, c, d, str, strarr);
		System.out.println(a+" "+b+" "+c[1]+" "+d[1]+" "+str+" "+strarr[1]);
//		Test t = new Test();
//		t.ParTest2(a, b, c, d, str, strarr);
//		System.out.println(a+" "+b+" "+c[1]+" "+d[1]+" "+str+" "+strarr[1]);

	}

}

1 c 4 s a string adsfasd

42.在做项目时，经常通过继承来简化和规范编程，因为经常要从数据库中提取数据，所以经常把数据库中的一个个表在项目中定义成实体类，其中有一个BaseEntity，被其他实体继承，其中包括每个表中共有的字段，比如修改时间，修改人等

package com.Entity;

import java.util.Date;

public abstract class BaseEntity {
	private String uId;//主键，用户ID
	private Date creationDate;//信息录入时间
	private Date modifiedDate;//最后一次修改的时间
	private String modifiedUserId;//最后一次修改的人的ID
	
	public String getuId() {
		return uId;
	}
	public void setuId(String uId) {
		this.uId = uId;
	}
	public Date getCreationDate() {
		return creationDate;
	}
	public void setCreationDate(Date creationDate) {
		this.creationDate = creationDate;
	}
	public Date getModifiedDate() {
		return modifiedDate;
	}
	public void setModifiedDate(Date modifiedDate) {
		this.modifiedDate = modifiedDate;
	}
	public String getModifiedUserId() {
		return modifiedUserId;
	}
	public void setModifiedUserId(String modifiedUserId) {
		this.modifiedUserId = modifiedUserId;
	}
}

package com.Entity;

public class T_Tel extends BaseEntity {
	private String telId;
	private String telNumber;
	
	public String getTelId() {
		return telId;
	}
	public void setTelId(String telId) {
		this.telId = telId;
	}
	public String getTelNumber() {
		return telNumber;
	}
	public void setTelNumber(String telNumber) {
		this.telNumber = telNumber;
	}
}

package com.Entity;

public class T_User extends BaseEntity {
	private String firstName;
	private String lastName;
	
	public String getFirstName() {
		return firstName;
	}
	public void setFirstName(String firstName) {
		this.firstName = firstName;
	}
	public String getLastName() {
		return lastName;
	}
	public void setLastName(String lastName) {
		this.lastName = lastName;
	}
}

package com.Dao;

import com.Entity.BaseEntity;

public abstract class BaseDao <T extends BaseEntity>{
	public abstract void insert(T t);
	public abstract void update(T t);
	public abstract T selectByPK(long PK);
	public abstract void delete(T t);
	public abstract void deleteByPK(long PK);
		
}

package com.Dao;

import com.Entity.T_Tel;

public class TelDao extends BaseDao<T_Tel> {

	@Override
	public void insert(T_Tel t) {
		// TODO Auto-generated method stub
		
	}

	@Override
	public void update(T_Tel t) {
		// TODO Auto-generated method stub
		
	}

	@Override
	public T_Tel selectByPK(long PK) {
		// TODO Auto-generated method stub
		return null;
	}

	@Override
	public void delete(T_Tel t) {
		// TODO Auto-generated method stub
		
	}

	@Override
	public void deleteByPK(long PK) {
		// TODO Auto-generated method stub
		
	}

}

package com.Dao;

import com.Entity.T_User;

public class UserDao extends BaseDao<T_User> {

	@Override
	public void insert(T_User t) {
		// TODO Auto-generated method stub
		
	}

	@Override
	public void update(T_User t) {
		// TODO Auto-generated method stub
		
	}

	@Override
	public T_User selectByPK(long PK) {
		// TODO Auto-generated method stub
		return null;
	}

	@Override
	public void delete(T_User t) {
		// TODO Auto-generated method stub
		
	}

	@Override
	public void deleteByPK(long PK) {
		// TODO Auto-generated method stub
		
	}

}

43.之前总是在想，学会了sql,我要怎么做到通过java代码从数据库提取出代码并显示在控制台，因为做网页或者很多项目经常需要把数据进行增删改查，并显示在网页中，别忘了需要导入connection的jar包

employee表是这个样子的

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

public class GetInfoFroDB {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		String url = "jdbc:mysql://localhost/activity";
		String user = "root";
		String password = "root";
		try {
			Class.forName("com.mysql.jdbc.Driver");
			Connection conn = DriverManager.getConnection(url, user, password);
			PreparedStatement pstmt = conn.prepareStatement("select firstname,lastname from employee where id > ?");
			pstmt.setString(1, "3");
			ResultSet rs = pstmt.executeQuery();
			while (rs.next()) {
				System.out.println(rs.getString(1) + " " + rs.getString(2));
			}
			pstmt.close();
			conn.close();
		} catch (ClassNotFoundException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (SQLException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}

}