Android -- 全局变量

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:padding="5dp">
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="40dp"
        android:orientation="horizontal">
        <TextView
            android:id="@+id/tv_name"
            android:layout_width="wrap_content"
            android:layout_height="match_parent"
            android:gravity="center"
            android:text="姓名："
            android:textColor="@color/black"
            android:textSize="17sp" />
        <EditText
            android:id="@+id/et_name"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_marginTop="3dp"
            android:layout_marginBottom="3dp"
            android:layout_weight="1"
            android:background="@drawable/edittext_select"
            android:hint="请输入姓名"
            android:inputType="text"
            android:maxLength="12"
            android:textColor="@color/black"
            android:textSize="17sp" />
    </LinearLayout>
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="40dp"
        android:orientation="horizontal">
        <TextView
            android:id="@+id/tv_age"
            android:layout_width="wrap_content"
            android:layout_height="match_parent"
            android:gravity="center"
            android:text="年龄："
            android:textColor="@color/black"
            android:textSize="17sp" />
        <EditText
            android:id="@+id/et_age"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_marginTop="3dp"
            android:layout_marginBottom="3dp"
            android:layout_weight="1"
            android:background="@drawable/edittext_select"
            android:hint="请输入年龄"
            android:inputType="number"
            android:maxLength="2"
            android:textColor="@color/black"
            android:textSize="17sp" />
    </LinearLayout>
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="40dp"
        android:orientation="horizontal">
        <TextView
            android:id="@+id/tv_height"
            android:layout_width="wrap_content"
            android:layout_height="match_parent"
            android:gravity="center"
            android:text="身高："
            android:textColor="@color/black"
            android:textSize="17sp" />
        <EditText
            android:id="@+id/et_height"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_marginTop="3dp"
            android:layout_marginBottom="3dp"
            android:layout_weight="1"
            android:background="@drawable/edittext_select"
            android:hint="请输入身高"
            android:inputType="number"
            android:maxLength="3"
            android:textColor="@color/black"
            android:textSize="17sp" />
    </LinearLayout>
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="40dp"
        android:orientation="horizontal">
        <TextView
            android:id="@+id/tv_weight"
            android:layout_width="wrap_content"
            android:layout_height="match_parent"
            android:gravity="center"
            android:text="体重："
            android:textColor="@color/black"
            android:textSize="17sp" />
        <EditText
            android:id="@+id/et_weight"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_marginTop="3dp"
            android:layout_marginBottom="3dp"
            android:layout_weight="1"
            android:background="@drawable/edittext_select"
            android:hint="请输入体重"
            android:inputType="numberDecimal"
            android:maxLength="5"
            android:textColor="@color/black"
            android:textSize="17sp" />
    </LinearLayout>
    <CheckBox
        android:id="@+id/ck_married"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:checked="false"
        android:gravity="center"
        android:text="已婚"
        android:textColor="@color/black"
        android:textSize="17sp" />
    <Button
        android:id="@+id/btn_save"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="保存"
        android:textColor="@color/black"
        android:textSize="17sp" />
</LinearLayout>

package com.example.datastorage;
import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.CheckBox;
import android.widget.EditText;
public class AppWriteActivity extends AppCompatActivity implements View.OnClickListener {
    private EditText et_name;
    private EditText et_age;
    private EditText et_height;
    private EditText et_weight;
    private CheckBox ck_married;
    private MyApplication app;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_app_write);
        et_name = findViewById(R.id.et_name);
        et_age = findViewById(R.id.et_age);
        et_height = findViewById(R.id.et_height);
        et_weight = findViewById(R.id.et_weight);
        ck_married = findViewById(R.id.ck_married);
        findViewById(R.id.btn_save).setOnClickListener(this);
        app = MyApplication.getInstance();
        reload();
    }
    private void reload() {
        String name = app.infoMap.get("name");
        if (name == null) {
            return;
        }
        String age = app.infoMap.get("age");
        String height = app.infoMap.get("height");
        String weight = app.infoMap.get("weight");
        String married = app.infoMap.get("married");
        et_name.setText(name);
        et_age.setText(age);
        et_height.setText(height);
        et_weight.setText(weight);
        if ("是".equals(married)) {
            ck_married.setChecked(true);
        } else {
            ck_married.setChecked(false);
        }
    }
    @Override
    public void onClick(View v) {
        String name = et_name.getText().toString();
        String age = et_age.getText().toString();
        String height = et_height.getText().toString();
        String weight = et_weight.getText().toString();
        app.infoMap.put("name", name);
        app.infoMap.put("age", age);
        app.infoMap.put("height", height);
        app.infoMap.put("weight", weight);
        app.infoMap.put("married", ck_married.isChecked() ? "是" : "否");
    }
}