code perfect

app/src/main/java/com/mxdl/faq/MainActivity.java

@@ -15,6 +15,7 @@ import android.support.v4.view.ViewPager;
 import android.support.v7.app.AppCompatActivity;
 import android.os.Bundle;
 import android.util.Log;
+import android.view.MotionEvent;
 import android.view.View;
 import android.widget.Button;
 import android.widget.PopupWindow;
@@ -79,8 +80,10 @@ public class MainActivity extends AppCompatActivity implements View.OnClickListe
 
         mTxtContent = findViewById(R.id.txt_content);
 
-        Intent intent ;
-
+        MotionEvent motionEvent = null;
+        float x = motionEvent.getX();
+        float y = motionEvent.getY();
+        float rawX = motionEvent.getRawX();
     }
 
     @Override

app/src/main/java/com/mxdl/faq/jvm/FinalizeEscapeGC.java

+package com.mxdl.faq.jvm;
+
+/**
+ * Description: <FinalizeEscapeGC><br>
+ * Author:      mxdl<br>
+ * Date:        2019/9/20<br>
+ * Version:     V1.0.0<br>
+ * Update:     <br>
+ */
+
+public class FinalizeEscapeGC {
+    public static FinalizeEscapeGC SAVE_HOOK = null;
+
+    @Override
+    protected void finalize() throws Throwable {
+        super.finalize();
+        System.out.println("finalize method executed!");
+        FinalizeEscapeGC.SAVE_HOOK = this;
+    }
+
+    public static void main(String[] args) throws InterruptedException {
+        // TODO Auto-generated method stub
+        SAVE_HOOK = new FinalizeEscapeGC();
+        kill();
+        //kill();
+
+    }
+
+    private static void kill() {
+        //下面这段代码与上面的完全相同，但是这次自救会失败
+        SAVE_HOOK = null;
+        System.gc();
+        //因为finalize方法的优先级很低，所以暂停0.5秒来等待它。
+        try {
+            Thread.sleep(500);
+        } catch (InterruptedException e) {
+            e.printStackTrace();
+        }
+        if (SAVE_HOOK != null) {
+            System.out.println("Yes,i'm alive.");
+        } else {
+            System.out.println("no,i am dead.");
+        }
+    }
+
+}

app/src/main/java/com/mxdl/faq/test/A.java

+package com.mxdl.faq.test;
+
+/**
+ * Description: <A><br>
+ * Author:      mxdl<br>
+ * Date:        2019/9/20<br>
+ * Version:     V1.0.0<br>
+ * Update:     <br>
+ */
+public interface A {
+    public void test();
+}

app/src/main/java/com/mxdl/faq/test/B.java

+package com.mxdl.faq.test;
+
+/**
+ * Description: <A><br>
+ * Author:      mxdl<br>
+ * Date:        2019/9/20<br>
+ * Version:     V1.0.0<br>
+ * Update:     <br>
+ */
+public interface B {
+    public void test();
+}

app/src/main/java/com/mxdl/faq/test/Test.java

@@ -6,6 +6,8 @@ import android.os.Bundle;
 import android.os.Message;
 import android.os.Messenger;
 
+import java.lang.ref.WeakReference;
+
 /**
  * Description: <Test><br>
  * Author:      mxdl<br>
@@ -13,12 +15,23 @@ import android.os.Messenger;
  * Version:     V1.0.0<br>
  * Update:     <br>
  */
-public class Test {
-    public void test(){
-        Message message;
-        Messenger messenger;
-        Bundle bundle;
-        Intent intent;
-        Bitmap bitmap;
+public class Test implements A,B{
+
+    @Override
+    public void test() {
+    }
+    public WeakReference<String> a(){
+        String str = new String("123");
+        WeakReference<String> weakReference = new WeakReference<>(str);
+        return weakReference;
+    }
+    public void b(){
+        WeakReference<String> b = a();
+        String s = b.get().toUpperCase();
+        System.out.println(s);
+    }
+    public static void main(String[] args){
+        Test test = new Test();
+        test.b();
     }
 }