Demo04-Tinh tuổi của bạn.

File String.xml

<resources>
    <string name="app_name">TinhTuoi</string>
    <string name="txttem">TinhTuoi</string>
    <string name="txthoten">Nhap Vao Ho Ten</string>
    <string name="ten">Name</string>
    <string name="namsinh">Nam Sinh</string>
    <string name="year">Year</string>
    <string name="btn">Tinh</string>
</resources>

File design layout:

<?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">

    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_margin="10dp"
        android:textSize="30sp"
        android:text="@string/txthoten" />

    <EditText
        android:id="@+id/edtten"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_margin="10dp"
        tools:ignore ="Autofill"
        android:hint="@string/ten"
        android:ems="10"
        android:inputType="textPersonName" />
    <TextView
        android:id="@+id/txtnamsinh"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_margin="10dp"
        android:textSize="30sp"
        android:text="@string/namsinh" />
    <EditText
        android:id="@+id/edtnamsinh"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_margin="10dp"
        tools:ignore ="Autofill"
        android:hint="@string/year"
        android:ems="10"
        android:inputType="textPersonName" />

    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_margin="10dp"
        android:textAllCaps="false"
        android:text="@string/btn" />
    <TextView
        android:id="@+id/txtkq"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_margin="10dp"
        android:textSize="30sp" />

</LinearLayout>

File sourcecode java.

package com.example.demo04;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

import org.w3c.dom.Text;

public class MainActivity extends AppCompatActivity {
    private Button btn;
    private EditText nam;
    private TextView ten,kq;
    private int namsinh;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);
        ten=(TextView)findViewById(R.id.edtten);
        nam=(EditText)findViewById(R.id.edtnamsinh);
        btn=(Button)findViewById(R.id.button);
        kq=(TextView)findViewById(R.id.txtkq);

        btn.setOnClickListener(new View.OnClickListener(){

            @Override
            public void onClick(View v) {
                namsinh =Integer.parseInt(nam.getText().toString());
                kq.setText(ten.getText().toString()+" "+ String.valueOf(2019-namsinh)+" tuoi");
            }
        });
    }
}