Simple Java Timer class.

Timer.java

package com.geoloqi.android.sdk.util;

import java.util.concurrent.TimeUnit;

/**
 * A simple class for timing short lived events.
 * 
 * @author Tristan Waddington
 */
public class Timer {
    private long mStart = 0;
    private long mEnd = 0;
    
    private boolean mRunning = true;
    
    private Timer(long now) {
        mStart = now;
    }
    
    @Override
    public String toString() {
        return getElapsedString(TimeUnit.SECONDS);
    }
    
    /**
     * Get the elapsed runtime in nanoseconds.
     * @return the runtime in nanoseconds.
     */
    public long getElapsed() {
        if (mRunning) {
            return System.nanoTime() - mStart;
        }
        return mEnd - mStart;
    }
    
    /**
     * Get the elapsed runtime in {@link TimeUnit}.
     * 
     * @param unit the desired unit.
     * @return the elapsed runtime converted from nanoseconds to the requested TimeUnit.
     */
    public double getElapsed(TimeUnit unit) {
        double elapsed = -1;
        
        switch(unit) {
        case SECONDS:
            elapsed = (double) getElapsed() / 1000000000.0;
            break;
        case MILLISECONDS:
            elapsed = (double) getElapsed() / 1000000.0;
            break;
        case NANOSECONDS:
            elapsed = getElapsed();
            break;
        }
        return elapsed;
    }
    
    /** Stub */
    public String getElapsedString(TimeUnit unit) {
        String u = "";
        switch(unit) {
        case SECONDS:
            u = "s";
            break;
        case MILLISECONDS:
            u = "ms";
            break;
        case NANOSECONDS:
            u = "ns";
            break;
        }
        return String.format("%s%s", getElapsed(unit), u);
    }
    
    /**
     * Stop the timer and return the elapsed runtime in nanoseconds.
     * @return the Timer object so methods can be chained.
     */
    public Timer end() {
        if (mRunning) {
            mEnd = System.nanoTime();
            mRunning = false;
        }
        return this;
    }
    
    /**
     * Start a new {@link Timer}.
     * @return a new Timer object.
     */
    public static Timer start() {
        return new Timer(System.nanoTime());
    }
}