<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".MainActivity">
 
    <ScrollView
        android:id="@+id/scrollView"
        android:layout_width="match_parent"
        android:layout_height="match_parent">
 
        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:descendantFocusability="blocksDescendants"
            android:orientation="vertical" >
 
            <Button
                android:id="@+id/buttonToDown"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:text="To Down" />
 
            <TextView
                android:id="@+id/textShow"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:text="" />
 
            <Button
                android:id="@+id/buttonToTop"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:text="To Top" />
 
        </LinearLayout>
    </ScrollView>
 
</LinearLayout>

package org.mk.android.demo.demoscrollview;
 
import androidx.appcompat.app.AppCompatActivity;
 
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.ScrollView;
import android.widget.TextView;
 
public class MainActivity extends AppCompatActivity {
    private Button btnDown;
    private Button btnUp;
    private ScrollView scrollView;
    private TextView txtShow;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        bindViews();
    }
    private void bindViews() {
        btnDown = (Button) findViewById(R.id.buttonToDown);
        btnUp = (Button) findViewById(R.id.buttonToTop);
        scrollView = (ScrollView) findViewById(R.id.scrollView);
        txtShow = (TextView) findViewById(R.id.textShow);
 
        StringBuilder sb = new StringBuilder();
        for (int i = 1; i <= 200; i++) {
            sb.append("呵呵 * " + i + "\n");
        }
        txtShow.setText(sb.toString());
        btnDown.setOnClickListener(new OnClickListener());
        btnUp.setOnClickListener(new OnClickListener());
    }
    private class OnClickListener implements View.OnClickListener{
        @Override
        public void onClick(View v){
            switch (v.getId()) {
                case R.id.buttonToDown:
                    //scrollView.fullScroll(ScrollView.FOCUS_DOWN);
                    scrollView.post(new Runnable() {
                        @Override
                        public void run() {
                            scrollView.fullScroll(ScrollView.FOCUS_DOWN);
                        }
                    });
                    break;
                case R.id.buttonToTop:
                    //scrollView.fullScroll(ScrollView.FOCUS_UP);
                    scrollView.post(new Runnable() {
                        @Override
                        public void run() {
                            scrollView.fullScroll(ScrollView.FOCUS_UP);
                        }
                    });
                    break;
            }
        }
    }
}