Exploring Hidden Java Costs (360|AnDev, July 2016)

Jake Wharton
Exploring
Java Hidden
Costs

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2?
0? 1?
How many methods?
class Example { 
}"

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How many methods?
class Example { 
}"
2?
0! 1?

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How many methods?
$ echo "class Example { 
}" > Example.java
2?
0! 1?

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How many methods?
}" > Example.java
$ javac Example.java
2?
0! 1?

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How many methods?
}" > Example.java
$ javap Example.class
2?
0! 1?

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How many methods?
}" > Example.java
class Example {
Example();
}
2?
0! 1?

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}" > Example.java
class Example {
Example();
}
How many methods?
}" > Example.java
class Example {
Example();
}
2?
0! 1?
How many methods? 0! 1? 2?

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}" > Example.java
class Example {
Example();
}
How many methods? 2?
0! 1!

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$ dx --dex --output=example.dex Example.class
0! 1!

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$ dexdump -f example.dex
0! 1!

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Opened 'example.dex', DEX version '035'
DEX file header:
magic : 'dex\n035\0'
checksum : b4e92dde
signature : f51f...a6a1
file_size : 436
header_size : 112
link_size : 0
link_off : 0 (0x000000)
string_ids_size : 5
string_ids_off : 112 (0x000070)
type_ids_size : 3
type_ids_off : 132 (0x000084)
proto_ids_size : 1
proto_ids_off : 144 (0x000090)
field_ids_size : 0
field_ids_off : 0 (0x000000)
method_ids_size : 2
method_ids_off : 156 (0x00009c)
class_defs_size : 1
class_defs_off : 172 (0x0000ac)
data_size : 232
data_off : 204 (0x0000cc)
0! 1!

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DEX file header:
checksum : b4e92dde
file_size : 436
header_size : 112
link_size : 0
link_off : 0 (0x000000)
string_ids_size : 5
type_ids_size : 3
type_ids_off : 132 (0x000084)
proto_ids_size : 1
field_ids_size : 0
method_ids_size : 2
class_defs_size : 1
data_size : 232
How many methods?
DEX file header:
checksum : b4e92dde
file_size : 436
header_size : 112
link_size : 0
link_off : 0 (0x000000)
string_ids_size : 5
type_ids_size : 3
type_ids_off : 132 (0x000084)
proto_ids_size : 1
field_ids_size : 0
method_ids_size : 2
class_defs_size : 1
data_size : 232
2?
0! 1!

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$ dex-method-list example.dex
0! 1!

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Example ()
java.lang.Object ()
0! 1!

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Example ()
java.lang.Object ()
$ javap -c Example.class
0! 1!

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Example ()
java.lang.Object ()
class Example {
Example();
Code:
0: aload_0
1: invokespecial #1 //java/lang/Object."":()V
4: return
}
0! 1!

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Example ()
java.lang.Object ()
class Example {
Example();
Code:
0: aload_0
4: return
}
0! 1!
Example ()
java.lang.Object ()
class Example {
Example();
Code:
0: aload_0
4: return
}
2?
0! 1!
How many methods?

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Example ()
java.lang.Object ()
class Example {
Example();
Code:
0: aload_0
4: return
}
How many methods? 2!
0! 1!

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How many methods?
2
0
1
class Example { 
}"
0 declared methods
0 in the source ﬁle

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How many methods?
2
1
class Example { 
}"
0 declared methods
0 in the source ﬁle
0 and only humans care

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How many methods?
2
class Example { 
}"
0 declared methods
1
1 compiled method
0 in the class ﬁle

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How many methods?
2
class Example { 
}"
0 declared methods
1 compiled method
2 referenced methods
0 in the dex ﬁle

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How many methods?
class Example { 
}3
0 declared methods
1 compiled method
2 referenced methods
0 in the dex ﬁle
0 for the true "method count"

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// Outer.java
public class OuterA{1
private class Example {2
}3 
}4

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// ItemsView.java
public class ItemsViewA{1
private class ItemsAdapter {2
}3 
}4
Outer
Outer
Example

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// ItemsView.java
public class ItemsView {
private class ItemsAdapter {
} 
}"
$ javac ItemsView.java

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// ItemsView.java
} 
}"
$ javac ItemsView.java
$ ls
ItemsView.class
ItemsView.java
ItemsView$ItemsAdapter.class

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// ItemsView.java
} 
}"
 
$ javap ItemsView
public ItemsView();
}

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// ItemsView.java
}G 
}"
 
$ javap 'ItemsView$ItemsAdapter'
class ItemsView$ItemsAdapter {
ItemsView$ItemsAdapter();
}
 
// ItemsAdapter.java

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// ItemsView.java
}G 
}"
 

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// ItemsView.java
public class ItemsView { 
}"
class ItemsAdapter {
}G

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// ItemsView.java
}"
// ItemsView$ItemsAdapter.java
class ItemsView$ItemsAdapter {
}G

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// ItemsView.java
}G 
}"
 
ItemsView$

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// ItemsView.java
private static String displayText(String item) { 
return ""; // TODO 
}L 
 
private class ItemsAdapter { 
}G 
}"

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// ItemsView.java
}L 
 
void bindItem(TextView tv, String item) { 
tv.setText(ItemsView.displayText(item)); 
}H 
}G 
}"
 
 
 
 
 
ItemsView$

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// ItemsView.java
}L 
 
}H 
}G 
}"

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// ItemsView.java
}L 
}"
 
class ItemsView$ItemsAdapter { 
}H 
}G
 
 
 
 
 
private

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// ItemsView.java
}L 
}"
 
}H 
}G
 
 
 
 
 
private
// ItemsView.java
} 
}"
 
} 
}

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// ItemsView.java
}L 
 
}H 
}G 
}"

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$ javac -bootclasspath android-sdk/platforms/android-24/android.jar \
ItemsView.java
$ javap -c 'ItemsView$ItemsAdapter'

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ItemsView.java
$ javap -c 'ItemsView$ItemsAdapter'
class ItemsView$ItemAdapter {
void bindItem(android.widget.TextView, java.lang.String);
Code:
0: aload_1
1: aload_2
2: invokestatic #3 // Method ItemsView.access$000:…
5: invokevirtual #4 // Method TextView.setText:…
8: return
}

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$ javap -p ItemsView

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$ javap -p ItemsView123
class ItemsView {
ItemsView();
private static java.lang.String displayText(…);
static java.lang.String access$000(…);
}
-c

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$ javap -p -c ItemsView123

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$ javap -p -c ItemsView123
class ItemsView {
ItemsView();
Code:
Code:
Code:
0: aload_0
1: invokestatic #1 // Method displayText:…
4: areturn
}

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$ javap -p -c ItemsView
class ItemsView {
ItemsView();
Code:
Code:
Code:
0: aload_0
1: invokestatic #1 // Method displayText:…
4: areturn
}

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// ItemsView.java
}B 
}A
 
}b 
}a

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// ItemsView.java
}B
static String access$000(String item) { 
return displayText(item); 
}C 
}A
 
}b 
}a
// ItemsView.java
}B
}C 
}A
 
}b 
}a

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// ItemsView.java
}B
}C 
}A
 
tv.setText(ItemsView.access$000(item)); 
}b 
}a
// ItemsView.java
}B
}C 
}A
 
tv.setText(ItemsView.access$000(item)); 
}b 
}a
 
 
 
 
 
 
 
 
displayText

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$ dx --dex --output=example.dex *.class

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ItemsView ()
ItemsView access$000(String) → String
ItemsView displayText(String) → String
ItemsView$ItemsAdapter (ItemsView)
ItemsView$ItemsAdapter bindItem(TextView, String)
android.widget.TextView setText(CharSequence)
java.lang.Object ()

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$ java -jar android-sdk/build-tools/24.0.1/jack.jar \
-cp android-sdk/platforms/android-24/android.jar \
--output-dex . \
ItemsView.java
$ dex-method-list classes.dex

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$ java -jar android-sdk/build-tools/24.0.1/jack.jar \
-cp android-sdk/platforms/android-24/android.jar \
--output-dex . \
ItemsView.java
ItemsView -wrap0(String) → String
ItemsView ()
ItemsView displayText(String) → String
java.lang.Object ()

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$ echo "-dontobfuscate
-keep class ItemsView$ItemsAdapter { void bindItem(...); }
" > rules.txt
$ java -jar proguard-base-5.2.1.jar \
-include rules.txt \
-injars . \
-outjars example-proguard.jar \
-libraryjars android-sdk/platforms/android-24/android.jar
$ dex-method-list example-proguard.jar

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$ echo "-dontobfuscate
-keep class ItemsView$ItemsAdapter { void bindItem(...); }
" > rules.txt
$ java -jar proguard-base-5.2.1.jar \
-include rules.txt \
-injars . \
-outjars example-proguard.jar \
-libraryjars android-sdk/platforms/android-24/android.jar

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ItemsView ()
java.lang.Object ()

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$ unzip example-proguard.jar
$ javap -c ItemsView

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$ javap -c ItemsView
public final class ItemsView {
static java.lang.String access$000(java.lang.String);
Code:
0: ldc #1 // String ""
2: areturn
}

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class MyActivity extends Activity { 
@Override protected void onCreate(Bundle state) { 
super.onCreate(state);
 
setContentView(R.layout.whatever); 
findViewById(R.id.button).setOnClickListener(
new OnClickListener() { 
@Override public void onClick(View view) { 
// Hello! 
} 
}); 
} 
}

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// Hello! 
}C 
}); 
}B 
}A

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doSomething();
}C 
}); 
}B
private void doSomething() { 
// ... 
}D 
}A
 
 
 
 
 
// Hello!

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private int count;
 
 
count = 0; 
++count; 
--count; 
count++; 
count--; 
Log.d("Count", "= " + count);
}C 
}); 
}B 
}A
 
 
 
 
 
 
doSomething();
 
 
private void doSomething() { 
// ... 
}D 

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private int count;
 
 
count = 0; 
++count; 
--count; 
count++; 
count--; 
Log.d("Count", "= " + count);
}C 
}); 
}B 
}A

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MyActivity.java
$ javap MyActivity

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MyActivity.java
$ javap MyActivity
class MyActivity extends android.app.Activity {
MyActivity();
protected void onCreate(android.os.Bundle);
static int access$002(MyActivity, int);
static int access$004(MyActivity);
}

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MyActivity.java
$ javap MyActivity
class MyActivity extends android.app.Activity {
MyActivity();
protected void onCreate(android.os.Bundle);
static int access$002(MyActivity, int);
}
// count = 0 write
// ++count preinc
// --count predec
// count++ postinc
// count-- postdec
// count read

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$ column -t -s $'\t' \
<(echo -e "NAME\tTOTAL\tMETHOD/READ\tWRITE\tPREINC\tPREDEC\tPOSTINC\tPOSTDEC\tOTHER" \
&& find apks -type f | \
xargs -L1 ./accessors.sh | \
sort -k2,2nr)
Warning: This may take a while to run!

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<(echo -e "NAME\tTOTAL\tMETHOD/READ\tWRITE\tPREINC\tPREDEC\tPOSTINC\tPOSTDEC\tOTHER" \
xargs -L1 ./accessors.sh | \
sort -k2,2nr)
NAME TOTAL METHOD/READ WRITE PREINC PREDEC POSTINC POSTDEC OTHER
com.amazon.avod.thirdpartyclient 5545 4963 506 0 0 9 5 62
com.amazon.kindle 5245 4399 789 0 0 11 4 42
com.amazon.mShop.android 4774 4091 593 2 0 42 6 40
com.audible.application 4357 3782 526 0 0 7 1 41
com.waze 4269 3544 675 0 0 18 4 28
com.amazon.mShop.android.shopping 3587 2968 536 3 0 38 5 37
me.lyft.android 3330 3111 200 0 1 2 1 15
com.nhl.gc1112.free 2796 2446 316 1 2 9 5 17
com.etrade.mobilepro.activity 2611 2327 273 0 0 2 1 8
air.com.nbcuni.com.nbcsports.liveextra 2448 2120 305 0 0 14 2 7
com.untappdllc.app 2314 2000 247 1 0 6 0 60
com.paypal.android.p2pmobile 2066 1771 286 1 0 2 0 6
com.google.android.apps.giant 1967 1747 199 0 0 6 3 12
com.netflix.mediaclient 1963 1642 294 1 0 9 2 15
com.stackexchange.marvin 1842 1386 260 0 0 6 2 188
net.flixster.android 1836 1583 239 0 0 6 2 6
com.Slack 1801 1571 215 0 0 5 2 8
com.showtime.showtimeanytime 1727 1450 250 0 0 4 4 19
com.google.android.apps.cloudconsole 1643 1464 168 0 0 1 2 8
com.eventbrite.attendee 1529 1368 147 0 0 2 0 12
org.videolan.vlc 1358 1163 151 0 0 2 1 41
com.imdb.mobile 1353 897 92 1 0 3 1 359
com.robinhood.android 1239 1036 149 0 0 4 0 50
com.twitter.android 1088 957 117 0 0 5 0 9

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}L 
 
}H 
}G 
}"

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static String displayText(String item) { 
}L 
 
}H 
}G 
}"

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interface Callback { 
void call(T value); 
}
 
 
 
class StringCallback implements Callback { 
@Override public void call(String value) { 
System.out.println(value); 
} 
}
// Callbacks.java

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$ javac Callbacks.java
$ javap StringCallback

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$ javac Callbacks.java
$ javap StringCallback
class StringCallback implements Callback {
StringCallback();
public void call(java.lang.String);
public void call(java.lang.Object);
}
-c

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$ javap -c StringCallback

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$ javap -c StringCallback
class StringCallback implements Callback {
StringCallback();
Code:
public void call(java.lang.String);
Code:
public void call(java.lang.Object);
Code:
0: aload_0
1: aload_1
2: checkcast #4 // class java/lang/String
5: invokevirtual #5 // Method call:(Ljava/lang/String;)V
8: return
}

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// Providers.java
 
 
 
 
 
 
class ViewProvider implements Provider { 
@Override public View get(Context context) { 
return new View(context); 
} 
}
 
 
interface Provider { 
T get(Context context); 
}

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Example.java
$ javap -c ViewProvider
class ViewProvider implements Provider {
ViewProvider();
Code:
public android.view.View get(android.content.Context);
Code:
public java.lang.Object get(android.content.Context);
Code:
0: aload_0
1: aload_1
2: invokevirtual #4 // Method get:(…)Landroid/view/View;
5: areturn
}

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// Providers.java
 
 
 
 
 
 
}2 
}3
 
 
interface Provider { 
T get(Context context); 
}

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}2 
}3
class TextViewProvider extends ViewProvider { 
@Override public TextView get(Context context) { 
return new TextView(context); 
} 
}

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} 
}
class TextViewProvider extends ViewProvider { 
@Override public TextView get(Context context) { 
return new TextView(context); 
} 
}

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$ javap TextViewProvider
class TextViewProvider extends ViewProvider {
TextViewProvider();
public android.widget.TextView get(android.content.Context);
public android.view.View get(android.content.Context);
public java.lang.Object get(android.content.Context);
}

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#!/usr/bin/python 
 
import os 
import subprocess 
import sys 
 
list = subprocess.check_output(["dex-method-list", sys.argv[1]]) 
 
class_info_by_name = {} 
 
for item in list.split('\n'): 
first_space = item.find(' ') 
open_paren = item.find('(') 
close_paren = item.find(')') 
last_space = item.rfind(' ') 
 
class_name = item[0:first_space] 
method_name = item[first_space + 1:open_paren] 
params = [param for param in item[open_paren + 1:close_paren].split(', ') if len(param) > 0] 
return_type = item[last_space + 1:] 
if last_space < close_paren: 
return_type = 'void' 
 
# print class_name, method_name, params, return_type 
 
if class_name not in class_info_by_name: 
class_info_by_name[class_name] = {} 
class_info = class_info_by_name[class_name] 
 
if method_name not in class_info: 
class_info[method_name] = [] 
method_info_by_name = class_info[method_name] 
 
method_info_by_name.append({ 
'params': params, 
'return': return_type 
}) 
 
count = 0 
for class_name, class_info in class_info_by_name.items(): 
for method_name, method_info_by_name in class_info.items(): 
for method_info in method_info_by_name: 
for other_method_info in method_info_by_name: 
if method_info == other_method_info: 
continue # Do not compare against self. 
params = method_info['params'] 
other_params = other_method_info['params'] 
if len(params) != len(other_params): 
continue # Do not compare different numbered parameter lists. 
 
match = True 
erased = False 
for idx, param in enumerate(params): 
other_param = other_params[idx] 
if param != 'Object' and not param[0].islower() and other_param == 'Object': 
erased = True 
elif param != other_param: 
match = False 
 
return_type = method_info['return'] 
other_return_type = other_method_info['return'] 
if return_type != 'Object' and other_return_type == 'Object': 
erased = True 
elif return_type != other_return_type: 
match = False 
 
if match and erased: 
count += 1 
# print "FOUND! %s %s %s %s" % (class_name, method_name, params, return_type) 
# print " %s %s %s %s" % (class_name, method_name, other_params, other_return_type) 
 
print os.path.basename(sys.argv[1]) + '\t' + str(count)
erased.py

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<(echo -e "NAME\tERASED" \
xargs -L1 ./erased.py | \
sort -k2,2nr)

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<(echo -e "NAME\tERASED" \
xargs -L1 ./erased.py | \
sort -k2,2nr)
NAME ERASED
com.amazon.mShop.android 4387
me.lyft.android 3269
com.amazon.avod.thirdpartyclient 2564
com.amazon.kindle 2439
com.imdb.mobile 2375
com.amazon.mShop.android.shopping 2259
com.nhl.gc1112.free 2178
com.Slack 2041
com.google.android.apps.giant 1971
com.ubercab 1877
com.squareup.cash 1819
com.twitter.android 1777
air.com.nbcuni.com.nbcsports.liveextra 1415
com.google.android.apps.docs.editors.slides 1378
com.audible.application 1206
com.robinhood.android 1196
com.foursquare.robin 1165
com.joelapenna.foursquared 1095
com.untappdllc.app 1091
com.google.android.apps.cloudconsole 1040
com.eventbrite.attendee 897

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class Greeter { 
void sayHi() { 
System.out.println("Hi!"); 
}1 
}2
 
 
 
 
class Example { 
public static void main(String... args) {
Executor executor = Executors.newSingleThreadExecutor(); 
Greeter greeter = new Greeter(); 
}5 
}6

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class Greeter { 
void sayHi() { 
}1 
}2
class Example { 
final Greeter greeter = new Greeter(); 
executor.execute(new Runnable() { 
@Override public void run() { 
greeter.sayHi(); 
}4 
}); 
}5 
}6

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class Greeter { 
void sayHi() { 
}1 
}2
class Example { 
executor.execute(() -> greeter.sayHi()); 
}5 
}6

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class Greeter { 
void sayHi() { 
}1 
}2
class Example { 
executor.execute(greeter::sayHi); 
}5 
}6

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$ javac *.java
Retrolambda toolchain
$ java -Dretrolambda.inputDir=. -Dretrolambda.classpath=. \ 
-jar retrolambda.jar
 
 

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$ javac *.java
Retrolambda toolchain
$ java -jar android-sdk/build-tools/24.0.1/jack.jar \ 
-cp android-sdk/platforms/android-24/android.jar \ 
--output-dex . *.java
Jack toolchain
$ java -Dretrolambda.inputDir=. -Dretrolambda.classpath=. \ 
-jar retrolambda.jar
 
 
 
 

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Code
Retrolambda
2.1.0
Retrolambda
2.3.0
Jack
24.0.1

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Code
Retrolambda
2.1.0
Retrolambda
2.3.0
Jack
24.0.1
new Runnable() { 
@Override
public void run() { 
greeter.sayHi(); 
} 
}
2 2 2

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Example ()
Example main(String[])
Example run(Runnable)
Example$1 (Greeter)
Example$1 run()
Greeter ()
Greeter sayHi()
java.io.PrintStream println(String)
java.lang.Object ()
java.lang.Runnable run()

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Example$1 (Greeter)
Example$1 run()

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Example$1 (Greeter)
Example$1 run()
$ javap -c 'Example$1'
final class Example$1 implements java.lang.Runnable {
Example$1(Greeter);
Code:
public void run();
Code:
0: aload_0
1: getfield #1 // Field val$greeter:LGreeter;
4: invokevirtual #3 // Method Greeter.sayHi:()V
7: return
}

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Code
Retrolambda
2.1.0
Retrolambda
2.3.0
Jack
24.0.1
new Runnable() { 
@Override
greeter.sayHi(); 
} 
}
2 2 2

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Code
Retrolambda
2.1.0
Retrolambda
2.3.0
Jack
24.0.1
new Runnable() { 
@Override
greeter.sayHi(); 
} 
}
2 2 2
() -> greeter.sayHi() 6 or 7 4 3

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Example ()
Example lambda$main$0(Greeter)
Example$$Lambda$1 (Greeter)
Example$$Lambda$1 lambdaFactory$(Greeter) → Runnable
Example$$Lambda$1 run()
Greeter ()
Greeter sayHi()
java.lang.Object ()
Retrolambda

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Retrolambda

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Retrolambda
$ javap -c Example
class Example {
static void lambda$main$0(Greeter);
Code:
0: aload_0
1: invokespecial #45 // Method sayHi:()V
4: return
}

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Retrolambda
$ javap -c 'Example$$Lambda$1'
final class Example$$Lambda$1 implements java.lang.Runnable {
public void run();
Code:
0: aload_0
1: getfield #15 // Field arg$1:LGreeter;
4: invokestatic #21 // Method Example.lambda$main$0:
7: return
}

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Retrolambda

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Example -Example_lambda$1(Greeter)
Example ()
Example$-void_main_java_lang_String__args_LambdaImpl0 (Greeter)
Example$-void_main_java_lang_String__args_LambdaImpl0 run()
Greeter ()
Greeter sayHi()
java.lang.Object ()
Jack

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Example -Example_lambda$1(Greeter)
Example$-void_main_java_lang_String__args_LambdaImpl0 (Greeter)
Example$-void_main_java_lang_String__args_LambdaImpl0 run()
Jack

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Code
Retrolambda
2.1.0
Retrolambda
2.3.0
Jack
24.0.1
new Runnable() { 
@Override
greeter.sayHi(); 
} 
}
2 2 2

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Code
Retrolambda
2.1.0
Retrolambda
2.3.0
Jack
24.0.1
new Runnable() { 
@Override
greeter.sayHi(); 
} 
}
2 2 2
greeter::sayHi 4 3 or 4 3

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<(echo -e "NAME\tRETROLAMBDA\tJACK" \
xargs -L1 ./lambdas.sh | \
sort -k2,2nr)

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<(echo -e "NAME\tRETROLAMBDA\tJACK" \
xargs -L1 ./lambdas.sh | \
sort -k2,2nr)
NAME RETROLAMBDA JACK
com.squareup.cash 826 0
com.robinhood.android 680 0
com.imdb.mobile 306 0
com.stackexchange.marvin 174 0
com.eventbrite.attendee 53 0
com.untappdllc.app 53 0

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HashMap
HashSet
HashMap
HashMap
HashMap
HashMap
HashMap
HashMap

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HashMap
HashSet
HashMap
HashMap
HashMap
HashMap
HashMap
HashMap
ArrayMap
ArraySet
SparseArray
SparseBooleanArray
SparseIntArray
SparseLongArray
LongSparseArray

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HashMap

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HashMap
int put(Integer, V)

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HashMap
int put(Integer, V)
getKey() int

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HashMap
int Integer.valueOf put(Integer, V)
getKey() int
Integer.intValue

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HashMap
Node[] table;
int size;

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HashMap
Node[] table;
int size;
...

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HashMap
Node[] table;
int size;
...
Node
int hash; 
K key; 
V value; 
Node next;

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HashMap
Node[] table;
int size;
...
Node
int hash; 
K key; 
V value; 
Node next;
Node
int hash; 
K key; 
V value; 
Node next;

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$ java -jar jol-cli-0.5-full.jar internals java.util.HashMap

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$ java -jar jol-cli-0.5-full.jar internals java.util.HashMap
# Running 64-bit HotSpot VM.
# Objects are 8 bytes aligned.
java.util.HashMap object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 01 00 00 00
4 4 (object header) 00 00 00 00
8 4 (object header) 9f 37 00 f8
12 4 Set AbstractMap.keySet null
16 4 Collection AbstractMap.values null
20 4 int HashMap.size 0
24 4 int HashMap.modCount 0
28 4 int HashMap.threshold 0
32 4 float HashMap.loadFactor 0.75
36 4 Node[] HashMap.table null
40 4 Set HashMap.entrySet null
44 4 (loss due to the next object alignment)
Instance size: 48 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total

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$ java -jar jol-cli-0.5-full.jar internals 'java.util.HashMap$Node'

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$ java -jar jol-cli-0.5-full.jar internals 'java.util.HashMap$Node'
java.util.HashMap$Node object internals:
0 12 (object header) N/A
12 4 int Node.hash N/A
16 4 Object Node.key N/A
20 4 Object Node.value N/A
24 4 Node Node.next N/A

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HashMap
Node[] table;
int size;
Node
int hash; 
K key; 
V value; 
Node next;

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HashMap
Node[] table;
int size;
Node
int hash; 
K key; 
V value; 
Node next;
48
HashMap object

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HashMap
Node[] table;
int size;
Node
int hash; 
K key; 
V value; 
Node next;
48 + 32 * entries
HashMap object
Node objects

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HashMap
Node[] table;
int size;
Node
int hash; 
K key; 
V value; 
Node next;
48 + 32 * entries + 4 * (entries / loadFactor) + 8
HashMap object
array of Node in HashMap
Node objects

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SparseArray
int[] keys;
V[] values;
int size;

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SparseArray
int[] keys;
V[] values;
int size;
...

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SparseArray
int[] keys;
V[] values;
int size;
...
...

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$ javac SparseArray.java
$ java -cp .:jol-cli-0.5-full.jar org.openjdk.jol.Main \ 
internals android.util.SparseArray

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$ javac SparseArray.java
$ java -cp .:jol-cli-0.5-full.jar org.openjdk.jol.Main \ 
internals android.util.SparseArray
android.util.SparseArray object internals:
0 4 (object header) 01 00 00 00
4 4 (object header) 00 00 00 00
8 4 (object header) 1a 69 01 f8
12 4 int SparseArray.mSize 0
16 1 boolean SparseArray.mGarbage false
17 3 (alignment/padding gap) N/A
20 4 int[] SparseArray.mKeys [0, 0, 0, 0, 0, 0, …]
24 4 Object[] SparseArray.mValues [null, null, null, …]

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SparseArray
int[] keys;
V[] values;
int size;

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SparseArray
int[] keys;
V[] values;
int size;
32
SparseArray object

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SparseArray
int[] keys;
V[] values;
int size;
32 + 4 * entries
SparseArray object
array of int keys

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SparseArray
int[] keys;
V[] values;
int size;
32 + 4 * entries + 4 * entries
SparseArray object
array of int keys array of V values

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SparseArray
int[] keys;
V[] values;
int size;
32 + (4 * entries + 4 * entries) / 0.75
SparseArray object
array of int keys array of V values binary tree fudge factor

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SparseArray
32 + (4 * entries + 4 * entries) / 0.75
HashMap
48 + 32 * entries + 4 * (entries / loadFactor) + 8

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SparseArray
32 + (4 * entries + 4 * entries) / 0.75
HashMap
48 + 32 * entries + 4 * (entries / 0.75) + 8

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SparseArray
32 + (4 * 50 + 4 * 50) / 0.75
HashMap
48 + 32 * 50 + 4 * (50 / 0.75) + 8

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SparseArray
32 + (4 * 50 + 4 * 50) / 0.75 = 656
HashMap
48 + 32 * 50 + 4 * (50 / 0.75) + 8 = 1922

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TODO (for you!)
• Turn on "private member" inspection in the IDE and listen to it.

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TODO (for you!)
• Report synthetic accessor methods in libraries as bugs.

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TODO (for you!)
• Update Retrolambda to 2.3.0 and try not to use it in open source libraries.

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TODO (for you!)
• Try using the Jack compiler in your app. Report failures to b.android.com.

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TODO (for you!)
• Try using the Jack compiler in your app. Report failures to b.android.com.
• Use ProGuard without overly-matchy rules (-keep class com.foo.**).

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Additional Presentations

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http://jakes.link/eliminate-overhead

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http://jakes.link/dex-ed

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http://jakes.link/android-perf

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Links
• Jack generates extra method for method references 
http://b.android.com/218301
• Retrolambda generates extra method for lambdas / method references 
https://github.com/orfjackal/retrolambda/issues/81
• dex-method-list tool for showing methods in class/jar/aar/dex/apk 
https://github.com/JakeWharton/dex-method-list
• Java Object Layout ("jol") tool for showing memory cost of types 
http://openjdk.java.net/projects/code-tools/jol/
• accessors.sh, erased.py, lambdas.sh helper scripts 
http://jakes.link/exploring-scripts

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Jake Wharton
Exploring
Java Hidden
Costs

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Exploring Hidden Java Costs (360|AnDev, July 2016)

Exploring Hidden Java Costs (360|AnDev, July 2016)

Jake Wharton
PRO

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Transcript

Exploring Hidden Java Costs (360|AnDev, July 2016)

Exploring Hidden Java Costs (360|AnDev, July 2016)

Jake Wharton PRO

More Decks by Jake Wharton

Other Decks in Programming

Featured

Transcript

Jake Wharton
PRO