Android : crash on android 5.0

Tool:

private static LruMemoryCache<String, SoftReference<Bitmap>>  mMemoryCache;
    private static final int sMinMemoryCacheSize =  1024 * 1024 * 2 ;  // 2MB
    private static  int sMemoryCacheSize = 1024 * 1024 * 4; // 4MB

    /**
     * @param memoryCacheSize
     */
    public static void setMemoryCacheSize(int memoryCacheSize){
        if( memoryCacheSize>=memoryCacheSize)
            sMemoryCacheSize= memoryCacheSize;
    }

    public static synchronized  LruMemoryCache<String, SoftReference<Bitmap>>  getLruMemoryCache(){

        if (mMemoryCache != null) {
            try {
                clearMemoryCache();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
        mMemoryCache = new LruMemoryCache<String, SoftReference<Bitmap>>(
                sMemoryCacheSize) {

            @Override
            protected int sizeOf(String key, SoftReference<Bitmap> bitmapRef) {
                return BitmapCommonUtils.getBitmapSize(bitmapRef.get());
            }
        };

        return mMemoryCache;
    }

    /**
     *clearMemoryCache
     */
    public synchronized static void clearMemoryCache() {
        if (mMemoryCache != null) {
            mMemoryCache.evictAll();
            // Add
            mMemoryCache=null;
        }
    }


    public synchronized static void addBitmapToMemoryCache(final String key, final Bitmap bitmap) {
        if (getBitmapFromMemoryCache(key) == null) {
            mMemoryCache.put(key,  new SoftReference<Bitmap>(bitmap));
        }
    }

    public synchronized static Bitmap getBitmapFromMemoryCache(final String key) {
        // Add
        if ( null == mMemoryCache)
            getLruMemoryCache();
        // Add
        if (mMemoryCache != null) {
            SoftReference<Bitmap> softRef = mMemoryCache.get(key);
                        return softRef == null ? null : softRef.get();
        }
        return null;
    }

ERR:

12-10 06:20:41.862: E/art(1680): Throwing OutOfMemoryError "Failed to allocate a 9938680 byte allocation with 5628604 free bytes and 5MB until OOM"

12-10 06:20:41.863: E/AndroidRuntime(1680): Error reporting crash

12-10 06:20:41.863: E/AndroidRuntime(1680): java.lang.OutOfMemoryError: Failed to allocate a 9938680 byte allocation with 5628604 free bytes and 5MB until OOM

12-10 06:20:41.863: E/AndroidRuntime(1680):     at java.lang.AbstractStringBuilder.enlargeBuffer(AbstractStringBuilder.java:95)

12-10 06:20:41.863: E/AndroidRuntime(1680):     at java.lang.AbstractStringBuilder.append0(AbstractStringBuilder.java:125)

12-10 06:20:41.863: E/AndroidRuntime(1680):     at java.lang.StringBuffer.append(StringBuffer.java:278)

12-10 06:20:41.863: E/AndroidRuntime(1680):     at java.io.StringWriter.write(StringWriter.java:123)

12-10 06:20:41.863: E/AndroidRuntime(1680):     at com.android.internal.util.FastPrintWriter.flushLocked(FastPrintWriter.java:358)

12-10 06:20:41.863: E/AndroidRuntime(1680):     at com.android.internal.util.FastPrintWriter.appendLocked(FastPrintWriter.java:303)

12-10 06:20:41.863: E/AndroidRuntime(1680):     at com.android.internal.util.FastPrintWriter.write(FastPrintWriter.java:625)

12-10 06:20:41.863: E/AndroidRuntime(1680):     at com.android.internal.util.FastPrintWriter.append(FastPrintWriter.java:658)

12-10 06:20:41.863: E/AndroidRuntime(1680):     at java.io.PrintWriter.append(PrintWriter.java:691)

12-10 06:20:41.863: E/AndroidRuntime(1680):     at java.io.PrintWriter.append(PrintWriter.java:31)

12-10 06:20:41.863: E/AndroidRuntime(1680):     at java.lang.Throwable.printStackTrace(Throwable.java:324)

12-10 06:20:41.863: E/AndroidRuntime(1680):     at java.lang.Throwable.printStackTrace(Throwable.java:300)

12-10 06:20:41.863: E/AndroidRuntime(1680):     at android.util.Log.getStackTraceString(Log.java:335)

12-10 06:20:41.863: E/AndroidRuntime(1680):     at com.android.internal.os.RuntimeInit.Clog_e(RuntimeInit.java:59)

12-10 06:20:41.863: E/AndroidRuntime(1680):     at com.android.internal.os.RuntimeInit.access$200(RuntimeInit.java:43)

12-10 06:20:41.863: E/AndroidRuntime(1680):     at com.android.internal.os.RuntimeInit$UncaughtHandler.uncaughtException(RuntimeInit.java:85)

12-10 06:20:41.863: E/AndroidRuntime(1680):     at java.lang.ThreadGroup.uncaughtException(ThreadGroup.java:693)

12-10 06:20:41.863: E/AndroidRuntime(1680):     at java.lang.ThreadGroup.uncaughtException(ThreadGroup.java:690)

this is my bitmap cache pool. it is fine on other version, but android 5.0. it is about ART question?

why bitmap cache will carsh on 5.0?