diff --git a/src/main/java/net/onrc/onos/core/topology/NetworkGraphImpl.java b/src/main/java/net/onrc/onos/core/topology/NetworkGraphImpl.java
index 902ffa6..a60e390 100644
--- a/src/main/java/net/onrc/onos/core/topology/NetworkGraphImpl.java
+++ b/src/main/java/net/onrc/onos/core/topology/NetworkGraphImpl.java
@@ -18,143 +18,143 @@
 import org.slf4j.LoggerFactory;
 
 public class NetworkGraphImpl implements NetworkGraph {
-	@SuppressWarnings("unused")
-	private static final Logger log = LoggerFactory.getLogger(NetworkGraphImpl.class);
+    @SuppressWarnings("unused")
+    private static final Logger log = LoggerFactory.getLogger(NetworkGraphImpl.class);
 
-	// DPID -> Switch
-	private ConcurrentMap<Long, Switch> switches;
+    // DPID -> Switch
+    private ConcurrentMap<Long, Switch> switches;
 
-	private ConcurrentMap<InetAddress, Set<Device>> addr2Device;
-	private ConcurrentMap<MACAddress, Device> mac2Device;
+    private ConcurrentMap<InetAddress, Set<Device>> addr2Device;
+    private ConcurrentMap<MACAddress, Device> mac2Device;
 
-	private ReadWriteLock readWriteLock = new ReentrantReadWriteLock();
-	private Lock readLock = readWriteLock.readLock();
-	// TODO use the write lock after refactor
-	private Lock writeLock = readWriteLock.writeLock();
+    private ReadWriteLock readWriteLock = new ReentrantReadWriteLock();
+    private Lock readLock = readWriteLock.readLock();
+    // TODO use the write lock after refactor
+    private Lock writeLock = readWriteLock.writeLock();
 
-	public NetworkGraphImpl() {
-		// TODO: Does these object need to be stored in Concurrent Collection?
-		switches = new ConcurrentHashMap<>();
-		addr2Device = new ConcurrentHashMap<>();
-		mac2Device = new ConcurrentHashMap<>();
-	}
+    public NetworkGraphImpl() {
+        // TODO: Does these object need to be stored in Concurrent Collection?
+        switches = new ConcurrentHashMap<>();
+        addr2Device = new ConcurrentHashMap<>();
+        mac2Device = new ConcurrentHashMap<>();
+    }
 
-	@Override
-	public Switch getSwitch(Long dpid) {
-		// TODO Check if it is safe to directly return this Object.
-		return switches.get(dpid);
-	}
+    @Override
+    public Switch getSwitch(Long dpid) {
+        // TODO Check if it is safe to directly return this Object.
+        return switches.get(dpid);
+    }
 
-	protected void putSwitch(Switch sw) {
-		switches.put(sw.getDpid(), sw);
-	}
+    protected void putSwitch(Switch sw) {
+        switches.put(sw.getDpid(), sw);
+    }
 
-	protected void removeSwitch(Long dpid) {
-		switches.remove(dpid);
-	}
+    protected void removeSwitch(Long dpid) {
+        switches.remove(dpid);
+    }
 
-	@Override
-	public Iterable<Switch> getSwitches() {
-		// TODO Check if it is safe to directly return this Object.
-		return Collections.unmodifiableCollection(switches.values());
-	}
+    @Override
+    public Iterable<Switch> getSwitches() {
+        // TODO Check if it is safe to directly return this Object.
+        return Collections.unmodifiableCollection(switches.values());
+    }
 
-	@Override
-	public Port getPort(Long dpid, Long number) {
-	    Switch sw = getSwitch(dpid);
-	    if (sw != null) {
-		return sw.getPort(number);
-	    }
-	    return null;
-	}
+    @Override
+    public Port getPort(Long dpid, Long number) {
+        Switch sw = getSwitch(dpid);
+        if (sw != null) {
+            return sw.getPort(number);
+        }
+        return null;
+    }
 
-	@Override
-	public Link getLink(Long dpid, Long number) {
-	    Port srcPort = getPort(dpid, number);
-	    if (srcPort == null)
-		return null;
-	    return srcPort.getOutgoingLink();
-	}
+    @Override
+    public Link getLink(Long dpid, Long number) {
+        Port srcPort = getPort(dpid, number);
+        if (srcPort == null)
+            return null;
+        return srcPort.getOutgoingLink();
+    }
 
-	@Override
-	public Link getLink(Long srcDpid, Long srcNumber, Long dstDpid,
-			    Long dstNumber) {
-	    Link link = getLink(srcDpid, srcNumber);
-	    if (link == null)
-		return null;
-	    if (!link.getDstSwitch().getDpid().equals(dstDpid))
-		return null;
-	    if (!link.getDstPort().getNumber().equals(dstNumber))
-		return null;
-	    return link;
-	}
+    @Override
+    public Link getLink(Long srcDpid, Long srcNumber, Long dstDpid,
+                        Long dstNumber) {
+        Link link = getLink(srcDpid, srcNumber);
+        if (link == null)
+            return null;
+        if (!link.getDstSwitch().getDpid().equals(dstDpid))
+            return null;
+        if (!link.getDstPort().getNumber().equals(dstNumber))
+            return null;
+        return link;
+    }
 
-	@Override
-	public Iterable<Link> getLinks() {
-		List<Link> linklist = new LinkedList<>();
+    @Override
+    public Iterable<Link> getLinks() {
+        List<Link> linklist = new LinkedList<>();
 
-		for (Switch sw : switches.values()) {
-			Iterable<Link> links = sw.getOutgoingLinks();
-			for (Link l : links) {
-				linklist.add(l);
-			}
-		}
-		return linklist;
-	}
+        for (Switch sw : switches.values()) {
+            Iterable<Link> links = sw.getOutgoingLinks();
+            for (Link l : links) {
+                linklist.add(l);
+            }
+        }
+        return linklist;
+    }
 
-	@Override
-	public Iterable<Device> getDevicesByIp(InetAddress ipAddress) {
-		Set<Device> devices = addr2Device.get(ipAddress);
-		if (devices == null) {
-			return Collections.emptySet();
-		}
-		return Collections.unmodifiableCollection(devices);
-	}
+    @Override
+    public Iterable<Device> getDevicesByIp(InetAddress ipAddress) {
+        Set<Device> devices = addr2Device.get(ipAddress);
+        if (devices == null) {
+            return Collections.emptySet();
+        }
+        return Collections.unmodifiableCollection(devices);
+    }
 
-	@Override
-	public Device getDeviceByMac(MACAddress address) {
-		return mac2Device.get(address);
-	}
+    @Override
+    public Device getDeviceByMac(MACAddress address) {
+        return mac2Device.get(address);
+    }
 
-	protected void putDevice(Device device) {
-	    mac2Device.put(device.getMacAddress(), device);
-	    for (InetAddress ipAddr : device.getIpAddress()) {
-		Set<Device> devices = addr2Device.get(ipAddr);
-		if (devices == null) {
-		    devices = new HashSet<>();
-		    addr2Device.put(ipAddr, devices);
-		}
-		devices.add(device);
-	    }
-	}
+    protected void putDevice(Device device) {
+        mac2Device.put(device.getMacAddress(), device);
+        for (InetAddress ipAddr : device.getIpAddress()) {
+            Set<Device> devices = addr2Device.get(ipAddr);
+            if (devices == null) {
+                devices = new HashSet<>();
+                addr2Device.put(ipAddr, devices);
+            }
+            devices.add(device);
+        }
+    }
 
-	protected void removeDevice(Device device) {
-	    mac2Device.remove(device.getMacAddress());
-	    for (InetAddress ipAddr : device.getIpAddress()) {
-		Set<Device> devices = addr2Device.get(ipAddr);
-		if (devices != null) {
-		    devices.remove(device);
-		    if (devices.isEmpty())
-			addr2Device.remove(ipAddr);
-		}
-	    }
-	}
+    protected void removeDevice(Device device) {
+        mac2Device.remove(device.getMacAddress());
+        for (InetAddress ipAddr : device.getIpAddress()) {
+            Set<Device> devices = addr2Device.get(ipAddr);
+            if (devices != null) {
+                devices.remove(device);
+                if (devices.isEmpty())
+                    addr2Device.remove(ipAddr);
+            }
+        }
+    }
 
-	@Override
-	public void acquireReadLock() {
-		readLock.lock();
-	}
+    @Override
+    public void acquireReadLock() {
+        readLock.lock();
+    }
 
-	@Override
-	public void releaseReadLock() {
-		readLock.unlock();
-	}
+    @Override
+    public void releaseReadLock() {
+        readLock.unlock();
+    }
 
-	protected void acquireWriteLock() {
-		writeLock.lock();
-	}
+    protected void acquireWriteLock() {
+        writeLock.lock();
+    }
 
-	protected void releaseWriteLock() {
-		writeLock.unlock();
-	}
+    protected void releaseWriteLock() {
+        writeLock.unlock();
+    }
 }