From cca025498432f408d14c6983c53f6d91371adf38 Mon Sep 17 00:00:00 2001
From: Cindy Zhang <cindyzyx9@gmail.com>
Date: Fri, 30 Dec 2016 09:32:28 -0800
Subject: [PATCH] implement singleton design pattern

---
 src/org/usfirst/frc/team3501/robot/OI.java       |  7 +++++++
 src/org/usfirst/frc/team3501/robot/Robot.java    | 16 +++++++++++-----
 .../team3501/robot/subsystems/DriveTrain.java    |  9 ++++++++-
 3 files changed, 26 insertions(+), 6 deletions(-)

diff --git a/src/org/usfirst/frc/team3501/robot/OI.java b/src/org/usfirst/frc/team3501/robot/OI.java
index 997be71..211c399 100644
--- a/src/org/usfirst/frc/team3501/robot/OI.java
+++ b/src/org/usfirst/frc/team3501/robot/OI.java
@@ -3,6 +3,7 @@ package org.usfirst.frc.team3501.robot;
 import edu.wpi.first.wpilibj.Joystick;
 
 public class OI {
+  private static OI oi;
   public static Joystick leftJoystick;
   public static Joystick rightJoystick;
 
@@ -11,4 +12,10 @@ public class OI {
     rightJoystick = new Joystick(Constants.OI.RIGHT_STICK_PORT);
 
   }
+  
+  public static OI getOI(){
+	  if(oi == null)
+		  oi = new OI();
+	  return oi;
+  }
 }
diff --git a/src/org/usfirst/frc/team3501/robot/Robot.java b/src/org/usfirst/frc/team3501/robot/Robot.java
index 36ca70b..3ccbadf 100644
--- a/src/org/usfirst/frc/team3501/robot/Robot.java
+++ b/src/org/usfirst/frc/team3501/robot/Robot.java
@@ -1,17 +1,23 @@
 package org.usfirst.frc.team3501.robot;
 
-import org.usfirst.frc.team3501.robot.Constants.DriveTrain;
+import org.usfirst.frc.team3501.robot.subsystems.DriveTrain;
 import edu.wpi.first.wpilibj.IterativeRobot;
 import edu.wpi.first.wpilibj.command.Scheduler;
 
 public class Robot extends IterativeRobot {
-  public static OI oi;
-  public static DriveTrain driveTrain;
 
   @Override
   public void robotInit() {
-    driveTrain = new DriveTrain();
-    oi = new OI();
+    DriveTrain.getDriveTrain();
+    OI.getOI();
+  }
+  
+  public static DriveTrain getDriveTrain(){
+	  return DriveTrain.getDriveTrain();
+  }
+  
+  public static OI getOI(){
+	  return OI.getOI();
   }
 
   @Override
diff --git a/src/org/usfirst/frc/team3501/robot/subsystems/DriveTrain.java b/src/org/usfirst/frc/team3501/robot/subsystems/DriveTrain.java
index 54b0ce0..6175630 100644
--- a/src/org/usfirst/frc/team3501/robot/subsystems/DriveTrain.java
+++ b/src/org/usfirst/frc/team3501/robot/subsystems/DriveTrain.java
@@ -5,14 +5,21 @@ import edu.wpi.first.wpilibj.CANTalon;
 import edu.wpi.first.wpilibj.command.Subsystem;
 
 public class DriveTrain extends Subsystem {
+  private static DriveTrain driveTrain;
   private CANTalon frontLeft, frontRight, rearLeft, rearRight;
 
-  public DriveTrain() {
+  private DriveTrain() {
     frontLeft = new CANTalon(Constants.DriveTrain.FRONT_LEFT);
     frontRight = new CANTalon(Constants.DriveTrain.FRONT_RIGHT);
     rearLeft = new CANTalon(Constants.DriveTrain.REAR_LEFT);
     rearRight = new CANTalon(Constants.DriveTrain.REAR_RIGHT);
   }
+  
+  public static DriveTrain getDriveTrain(){
+	  if(driveTrain == null)
+		  driveTrain = new DriveTrain();
+	  return driveTrain;
+  }
 
   @Override
   protected void initDefaultCommand() {
-- 
2.30.2