diff --git a/RootActivity.java b/RootActivity.java
new file mode 100644
index 0000000..97559b9
--- /dev/null
+++ b/RootActivity.java
@@ -0,0 +1,96 @@
+package com.example.drink_order_system;
+
+import android.annotation.SuppressLint;
+import android.app.Fragment;
+import android.app.FragmentManager;
+import android.app.FragmentTransaction;
+import android.os.Bundle;
+import android.util.Log;
+import android.widget.RadioButton;
+import android.widget.RadioGroup;
+
+import androidx.appcompat.app.AppCompatActivity;
+
+public class RootActivity extends AppCompatActivity {
+
+    private RadioGroup rg_tab_bar;
+    private RadioButton rb_order;
+    private Fragment fg_order; //点单界面
+    private Fragment fg_mine; //个人信息界面
+    private Fragment fg_bill; //查看历史订单界面
+    private FragmentManager fManager;
+    private String userName;
+
+    @SuppressLint("MissingInflatedId")
+    @Override
+    protected void onCreate(Bundle savedInstanceState) {
+        super.onCreate(savedInstanceState);
+        setContentView(R.layout.activity_root);
+        userName = getIntent().getStringExtra("userName");
+        System.out.println("username in oncreate in rootActivity "+userName);
+        fManager = getFragmentManager();
+        rg_tab_bar = (RadioGroup) findViewById(R.id.rg_tab);
+        rg_tab_bar.setOnCheckedChangeListener(this::onCheckedChanged); //对下方导航栏设置监听，实现界面切换
+        //获取第一个单选按钮，并设置其为选中状态
+        rb_order = (RadioButton) findViewById(R.id.rb_order);
+        rb_order.setChecked(true);
+        defaultFragment(); //将点单界面设为默认界面
+    }
+
+    public void defaultFragment()
+    {
+        FragmentTransaction fTransaction = fManager.beginTransaction();
+        fg_order = new RestaurantFragment(userName);
+        fTransaction.add(R.id.ly_content,fg_order);
+        fTransaction.show(fg_order);
+        fTransaction.commit();
+    }
+
+    public void onCheckedChanged(RadioGroup group, int checkedId) { //界面切换函数
+        FragmentTransaction fTransaction = fManager.beginTransaction();
+        hideAllFragment(fTransaction); //先隐藏所有界面
+            switch (checkedId){
+                case R.id.rb_order:
+                    if(fg_order==null)
+                    {
+                        fg_order = (Fragment) new RestaurantFragment(userName);
+                        fTransaction.add(R.id.ly_content,fg_order);
+                        fTransaction.show(fg_order);
+                    }
+                    else
+                        fTransaction.show(fg_order);
+                    break;
+                case R.id.rb_bill:
+                    if(fg_bill==null)
+                    {
+                        fg_bill = BillFragment.newInstance(userName);
+                        fTransaction.add(R.id.ly_content,fg_bill);
+                        fTransaction.show(fg_bill);
+                    }
+                    else
+                        fTransaction.show(fg_bill);
+                    break;
+                case R.id.rb_mine:
+                    if(fg_mine==null)
+                    {
+                        fg_mine = MineFragment.newInstance(userName);
+                    //    Log.e("fg_mine",userName);
+                        fTransaction.add(R.id.ly_content,fg_mine);
+                        fTransaction.show(fg_mine);
+                    }
+                    else
+                        fTransaction.show(fg_mine);
+                    break;
+            }
+        fTransaction.commit();
+    }
+
+    //隐藏所有Fragment
+    private void hideAllFragment(FragmentTransaction fragmentTransaction){
+        if(fg_order!=null)fragmentTransaction.hide(fg_order);
+        if(fg_bill!=null)fragmentTransaction.hide(fg_bill);
+        if(fg_mine!=null)fragmentTransaction.hide(fg_mine);
+    }
+
+
+}
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