源碼：
/frameworks/base/core/java/android/util/DisplayMetrics.java
194 /**
195 * The logical density of the display. This is a scaling factor for the
196 * Density Independent Pixel unit, where one DIP is one pixel on an
197 * approximately 160 dpi screen (for example a 240x320, 1.5"x2" screen),
198 * providing the baseline of the system's display. Thus on a 160dpi screen
199 * this density value will be 1; on a 120 dpi screen it would be .75; etc.
200 *
201 * <p>This value does not exactly follow the real screen size (as given by
202 * {@link #xdpi} and {@link #ydpi}, but rather is used to scale the size of
203 * the overall UI in steps based on gross changes in the display dpi. For
204 * example, a 240x320 screen will have a density of 1 even if its width is
205 * 1.8", 1.3", etc. However, if the screen resolution is increased to
206 * 320x480 but the screen size remained 1.5"x2" then the density would be
207 * increased (probably to 1.5).
208 *
209 * @see #DENSITY_DEFAULT
210 */
211 public float density;
默認：
299 public void setToDefaults() {
300 widthPixels = 0;
301 heightPixels = 0;
302 density = DENSITY_DEVICE / (float) DENSITY_DEFAULT;
303 densityDpi = DENSITY_DEVICE;
304 scaledDensity = density;
305 xdpi = DENSITY_DEVICE;
306 ydpi = DENSITY_DEVICE;
307 noncompatWidthPixels = widthPixels;
308 noncompatHeightPixels = heightPixels;
309 noncompatDensity = density;
310 noncompatDensityDpi = densityDpi;
311 noncompatScaledDensity = scaledDensity;
312 noncompatXdpi = xdpi;
313 noncompatYdpi = ydpi;
314 }
註釋：
默認情況：density = DENSITY_DEVICE / (float) DENSITY_DEFAULT;
DENSITY_DEVICE和DENSITY_DEFAULT在DisplayMetrics.java都有說明：
35 /**
36 * Standard quantized DPI for medium-density screens.
37 */
38 public static final int DENSITY_MEDIUM = 160;
...
155 public static final int DENSITY_DEFAULT = DENSITY_MEDIUM;
...
162
163 /**
164 * The device's current density.
165 * <p>
166 * This value reflects any changes made to the device density. To obtain
167 * the device's stable density, use {@link #DENSITY_DEVICE_STABLE}.
168 *
169 * @hide This value should not be used.
170 * @deprecated Use {@link #DENSITY_DEVICE_STABLE} to obtain the stable
171 * device density or {@link #densityDpi} to obtain the current
172 * density for a specific display.
173 */
174 @Deprecated
175 public static int DENSITY_DEVICE = getDeviceDensity();
...
370 private static int getDeviceDensity() {
371 // qemu.sf.lcd_density can be used to override ro.sf.lcd_density
372 // when running in the emulator, allowing for dynamic configurations.
373 // The reason for this is that ro.sf.lcd_density is write-once and is
374 // set by the init process when it parses build.prop before anything else.
375 return SystemProperties.getInt("qemu.sf.lcd_density",
376 SystemProperties.getInt("ro.sf.lcd_density", DENSITY_DEFAULT));
377 }
即：dpi爲160時，density爲1