Basic PostgreSQL/Java example

DBGuy.java

import java.sql.*;

public class DBGuy {
	private Connection c = null;
	
	public DBGuy() {
		try {
			Class.forName("org.postgresql.Driver");
			c = DriverManager
					.getConnection("jdbc:postgresql://localhost:5432/testdb",
							"user", "pass");
		} catch(Exception e) {
			e.printStackTrace();
			System.exit(0);
		}
		System.out.println("Opened database sucessfully.");
	}
	
	public void createCompanyTable() {
		Statement s = null;
		try {
			s = c.createStatement();
			String sql = "CREATE TABLE COMPANY (" +
						 "ID INT PRIMARY KEY	NOT NULL," +
						 "NAME			TEXT	NOT NULL," +
						 "AGE			INT		NOT NULL," +
						 "ADDRESS		CHAR(50)," + 
						 "SALARY		REAL)";
			s.executeUpdate(sql);
			s.close();
		} catch(Exception e) {
			e.printStackTrace();
			System.exit(0);
		}
		System.out.println("Company table created successfully.");
	}
	
	public void deleteCompanyTable() {
		Statement s = null;
		try {
			s = c.createStatement();
			String sql = "DROP TABLE IF EXISTS COMPANY";
			s.execute(sql);
		} catch(Exception e) {
			e.printStackTrace();
			System.exit(0);
		}
	}
	
	public void closeConnection() {
		try {
			c.close();
		} catch (Exception e) {
			e.printStackTrace();
			System.exit(0);
		}
		System.out.println("Connection closed.");
	}
}

HelloWorld.java

/*
https://www.tutorialspoint.com/postgresql/postgresql_java.htm
http://www.cheat-sheets.org/sites/sql.su/

PRIMARY KEY
The primary key consists of one or more columns
whose data contained within is used to uniquely
identify each row in the table. You can think of
the primary key as an address. If the rows in a
table were mailboxes, then the primary key would
be the listing of street addresses.

FOREIGN KEY
A foreign key is a set of one or more columns in
a table that refers to the primary key in another
table.

SQL EXAMPLE
CREATE TABLE Orders
(
O_Id int NOT NULL,
OrderNo int NOT NULL,
P_Id int,
PRIMARY KEY (O_Id),
FOREIGN KEY (P_Id) REFERENCES Persons(P_Id)
)
*/

public class HelloWorld {
	public static void main(String[] args) {
		DBGuy dbg = new DBGuy();
		dbg.deleteCompanyTable();
		dbg.createCompanyTable();
	}
}