activity_main.xmlMainActivity.java
<?xml version="1.0" encoding="utf-8"?> <RelativeLayout 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:padding="16dp" tools:context="com.codinginflow.additionexample.MainActivity"> <EditText android:id="@+id/edittext_number_1" android:layout_width="match_parent" android:layout_height="wrap_content" android:inputType="number" /> <EditText android:id="@+id/edittext_number_2" android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_alignParentStart="true" android:layout_below="@+id/edittext_number_1" android:inputType="number" /> <TextView android:id="@+id/textview_result" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_below="@+id/edittext_number_2" android:layout_centerHorizontal="true" android:layout_marginTop="16dp" android:text="0" android:textColor="@android:color/black" android:textSize="50sp" /> <Button android:id="@+id/button_add" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_centerHorizontal="true" android:layout_centerVertical="true" android:text="add" /> </RelativeLayout>
package com.codinginflow.additionexample; 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; public class MainActivity extends AppCompatActivity { private EditText mEditText1; private EditText mEditText2; private TextView mTextViewResult; private Button mButtonAdd; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); mEditText1 = findViewById(R.id.edittext_number_1); mEditText2 = findViewById(R.id.edittext_number_2); mTextViewResult = findViewById(R.id.textview_result); mButtonAdd = findViewById(R.id.button_add); mButtonAdd.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { if (mEditText1.getText().toString().length() == 0) { mEditText1.setText("0"); } if (mEditText2.getText().toString().length() == 0) { mEditText2.setText("0"); } int num1 = Integer.parseInt(mEditText1.getText().toString()); int num2 = Integer.parseInt(mEditText2.getText().toString()); int sum = num1 + num2; mTextViewResult.setText(String.valueOf(sum)); } }); } }