StopWatchTree.java

import java.util.LinkedList;
import java.util.concurrent.TimeUnit;


public class StopWatchTree 
{
	private final String name;
	private final long startNanoTime;
	private final LinkedList<StopWatchTree> children;	
	
	private boolean isRunning;
	private long elapsedNanos;

	
	public StopWatchTree(String name)
	{
		this.name = name;
		this.startNanoTime = System.nanoTime();				
		this.children = new LinkedList<>();
		this.isRunning = true;
	}
	
	private void checkIsRunning()
	{
		if (!isRunning) 
		{
			throw new IllegalArgumentException("StopWatch is not running");
		}		
	}
	
	public void start(String name) 
	{
		checkIsRunning();
		
		if (!children.isEmpty() && children.getLast().isRunning)
		{
			children.getLast().start(name);
		}
		else 
		{
			children.add(new StopWatchTree(name));
		}
	}
	
	public void stop()
	{
		checkIsRunning();
		
		if (!children.isEmpty() && children.getLast().isRunning)
		{
			children.getLast().stop();
		}
		else
		{
			elapsedNanos = System.nanoTime() - startNanoTime;			
			isRunning = false;
		}
	}
	
	public String toString()
	{
		return toString(TimeUnit.MICROSECONDS);
	}
	
	public String toString(TimeUnit timeUnit)
	{
		StringBuilder builder = new StringBuilder();
		toString(builder, timeUnit, 0, "");
		return builder.toString();		
	}
	
	private void toString(StringBuilder builder, TimeUnit timeUnit, int level, String treeChar)
	{
		for (int i = level; i > 0; i--) 
		{
			if (i == 1) builder.append(treeChar);
			else builder.append("|");
		}
		
		long actualElapsedNanos = isRunning ? System.nanoTime() - startNanoTime : elapsedNanos;
		
		builder.append(name).append("[").append(Long.toString(timeUnit.convert(actualElapsedNanos, TimeUnit.NANOSECONDS))).append("]");
		builder.append("\n");
		
		StopWatchTree last = children.isEmpty() ? null : children.getLast();
		for (StopWatchTree child : children)
		{
			child.toString(builder, timeUnit, level + 1, child == last ? "\\" : "+");
		}
	}
}