Understanding of @hide

In the previous article "Learning HandlerThread" , we mentioned that although there is a getThreadHandler() method in the HandlerThread class to get the Handler, it is impossible for us to call it . Because this method is @hideannotated with

/**
     * @return a shared {@link Handler} associated with this thread
     * @hide
     */
    @NonNull
    public Handler getThreadHandler() {
    
    
        if (mHandler == null) {
    
    
            mHandler = new Handler(getLooper());
        }
        return mHandler;
    }

So let's take a look at @hidewhat is sacred.

If the build.gradle of our android project is configured compileSdk 32, then when we compile our android application, $ANDROID_SDK_HOME/platforms/android-32/android.jarit will be added to our compile-time classpath and participate in the compilation of the app. @hideIt will control the things in the android.jar package we use when compiling.

android.jar is created as part of compiling android itself. Android framework classes are analyzed and copies of them are created. This copy has the following characteristics:

• Remove marked @hideclasses, methods, fields, etc.
• All remaining methods have stub implementations, namelythrow new RuntimeException("Stub!")
• Keep JavaDoc annotations of all classes, methods, and fields that have not been removed

Let's use the javap command to check the contents of android.os.HandlerThread.class:

% javap -verbose android/os/HandlerThread.class

From the following we can see that HandlerThread.class does not have a getThreadHandler method.

Classfile 
***/adddd/android/android/os/HandlerThread.class
  Last modified Jan 1, 2008; size 1043 bytes
  SHA-256 checksum 8161f60748df5cf7489dbf189c3f4668d81a17595dbd55e52baa0f8263bb96d4
  Compiled from "HandlerThread.java"
public class android.os.HandlerThread extends java.lang.Thread
  minor version: 0
  major version: 52
  flags: (0x0021) ACC_PUBLIC, ACC_SUPER
  this_class: #5                          // android/os/HandlerThread
  super_class: #6                         // java/lang/Thread
  interfaces: 0, fields: 0, methods: 8, attributes: 1
Constant pool:
   #1 = Methodref          #6.#31         // java/lang/Thread."<init>":()V
   #2 = Class              #32            // java/lang/RuntimeException
   #3 = String             #33            // Stub!
   #4 = Methodref          #2.#34         // java/lang/RuntimeException."<init>":(Ljava/lang/String;)V
   #5 = Class              #35            // android/os/HandlerThread
   #6 = Class              #36            // java/lang/Thread
   #7 = Utf8               <init>
   #8 = Utf8               (Ljava/lang/String;)V
   #9 = Utf8               Code
  #10 = Utf8               LineNumberTable
  #11 = Utf8               LocalVariableTable
  #12 = Utf8               this
  #13 = Utf8               Landroid/os/HandlerThread;
  #14 = Utf8               name
  #15 = Utf8               Ljava/lang/String;
  #16 = Utf8               (Ljava/lang/String;I)V
  #17 = Utf8               priority
  #18 = Utf8               I
  #19 = Utf8               onLooperPrepared
  #20 = Utf8               ()V
  #21 = Utf8               run
  #22 = Utf8               getLooper
  #23 = Utf8               ()Landroid/os/Looper;
  #24 = Utf8               quit
  #25 = Utf8               ()Z
  #26 = Utf8               quitSafely
  #27 = Utf8               getThreadId
  #28 = Utf8               ()I
  #29 = Utf8               SourceFile
  #30 = Utf8               HandlerThread.java
  #31 = NameAndType        #7:#20         // "<init>":()V
  #32 = Utf8               java/lang/RuntimeException
  #33 = Utf8               Stub!
  #34 = NameAndType        #7:#8          // "<init>":(Ljava/lang/String;)V
  #35 = Utf8               android/os/HandlerThread
  #36 = Utf8               java/lang/Thread
{
    
    
  public android.os.HandlerThread(java.lang.String);
    descriptor: (Ljava/lang/String;)V
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=3, locals=2, args_size=2
         0: aload_0
         1: invokespecial #1                  // Method java/lang/Thread."<init>":()V
         4: new           #2                  // class java/lang/RuntimeException
         7: dup
         8: ldc           #3                  // String Stub!
        10: invokespecial #4                  // Method java/lang/RuntimeException."<init>":(Ljava/lang/String;)V
        13: athrow
      LineNumberTable:
        line 23: 0
      LocalVariableTable:
        Start  Length  Slot  Name   Signature
            0      14     0  this   Landroid/os/HandlerThread;
            0      14     1  name   Ljava/lang/String;

  public android.os.HandlerThread(java.lang.String, int);
    descriptor: (Ljava/lang/String;I)V
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=3, locals=3, args_size=3
         0: aload_0
         1: invokespecial #1                  // Method java/lang/Thread."<init>":()V
         4: new           #2                  // class java/lang/RuntimeException
         7: dup
         8: ldc           #3                  // String Stub!
        10: invokespecial #4                  // Method java/lang/RuntimeException."<init>":(Ljava/lang/String;)V
        13: athrow
      LineNumberTable:
        line 25: 0
      LocalVariableTable:
        Start  Length  Slot  Name   Signature
            0      14     0  this   Landroid/os/HandlerThread;
            0      14     1  name   Ljava/lang/String;
            0      14     2 priority   I

  protected void onLooperPrepared();
    descriptor: ()V
    flags: (0x0004) ACC_PROTECTED
    Code:
      stack=3, locals=1, args_size=1
         0: new           #2                  // class java/lang/RuntimeException
         3: dup
         4: ldc           #3                  // String Stub!
         6: invokespecial #4                  // Method java/lang/RuntimeException."<init>":(Ljava/lang/String;)V
         9: athrow
      LineNumberTable:
        line 27: 0
      LocalVariableTable:
        Start  Length  Slot  Name   Signature
            0      10     0  this   Landroid/os/HandlerThread;

  public void run();
    descriptor: ()V
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=3, locals=1, args_size=1
         0: new           #2                  // class java/lang/RuntimeException
         3: dup
         4: ldc           #3                  // String Stub!
         6: invokespecial #4                  // Method java/lang/RuntimeException."<init>":(Ljava/lang/String;)V
         9: athrow
      LineNumberTable:
        line 29: 0
      LocalVariableTable:
        Start  Length  Slot  Name   Signature
            0      10     0  this   Landroid/os/HandlerThread;

  public android.os.Looper getLooper();
    descriptor: ()Landroid/os/Looper;
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=3, locals=1, args_size=1
         0: new           #2                  // class java/lang/RuntimeException
         3: dup
         4: ldc           #3                  // String Stub!
         6: invokespecial #4                  // Method java/lang/RuntimeException."<init>":(Ljava/lang/String;)V
         9: athrow
      LineNumberTable:
        line 31: 0
      LocalVariableTable:
        Start  Length  Slot  Name   Signature
            0      10     0  this   Landroid/os/HandlerThread;

  public boolean quit();
    descriptor: ()Z
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=3, locals=1, args_size=1
         0: new           #2                  // class java/lang/RuntimeException
         3: dup
         4: ldc           #3                  // String Stub!
         6: invokespecial #4                  // Method java/lang/RuntimeException."<init>":(Ljava/lang/String;)V
         9: athrow
      LineNumberTable:
        line 33: 0
      LocalVariableTable:
        Start  Length  Slot  Name   Signature
            0      10     0  this   Landroid/os/HandlerThread;

  public boolean quitSafely();
    descriptor: ()Z
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=3, locals=1, args_size=1
         0: new           #2                  // class java/lang/RuntimeException
         3: dup
         4: ldc           #3                  // String Stub!
         6: invokespecial #4                  // Method java/lang/RuntimeException."<init>":(Ljava/lang/String;)V
         9: athrow
      LineNumberTable:
        line 35: 0
      LocalVariableTable:
        Start  Length  Slot  Name   Signature
            0      10     0  this   Landroid/os/HandlerThread;

  public int getThreadId();
    descriptor: ()I
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=3, locals=1, args_size=1
         0: new           #2                  // class java/lang/RuntimeException
         3: dup
         4: ldc           #3                  // String Stub!
         6: invokespecial #4                  // Method java/lang/RuntimeException."<init>":(Ljava/lang/String;)V
         9: athrow
      LineNumberTable:
        line 37: 0
      LocalVariableTable:
        Start  Length  Slot  Name   Signature
            0      10     0  this   Landroid/os/HandlerThread;
}
SourceFile: "HandlerThread.java"

Here is another introduction to some information seen from this HandlerThread.class:

• minor version: 0 major version: 52: Indicates which compiler is used to produce the current .class file

JDK Version	(in Decimal) Major Version
Java SE 8.0	52
Java SE 11.0	55

• Compiled from "HandlerThread.java": Indicates that the .class file is compiled from this "HandlerThread.java"