Write a Android code to calculate area of triangle:

Activity_main.xml

<?xml version="1.0" encoding="utf-8"?>

<androidx.constraintlayout.widget.ConstraintLayout 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"
tools:context=".MainActivity">

<EditText
    android:id="@+id/num1"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginStart="92dp"
    android:layout_marginTop="51dp"
    android:layout_marginEnd="109dp"
    android:layout_marginBottom="37dp"
    android:ems="10"
    android:inputType="number"
    app:layout_constraintBottom_toTopOf="@+id/num2"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent"
    tools:ignore="SpeakableTextPresentCheck,TouchTargetSizeCheck" />

<EditText
    android:id="@+id/num2"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginStart="92dp"
    android:layout_marginTop="37dp"
    android:layout_marginEnd="109dp"
    android:layout_marginBottom="58dp"
    android:ems="10"
    android:inputType="number"
    app:layout_constraintBottom_toTopOf="@+id/num3"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toBottomOf="@+id/num1"
    tools:ignore="SpeakableTextPresentCheck,TouchTargetSizeCheck" />

<EditText
    android:id="@+id/num3"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginStart="90dp"
    android:layout_marginTop="39dp"
    android:layout_marginEnd="111dp"
    android:layout_marginBottom="41dp"
    android:ems="10"
    android:inputType="number"
    app:layout_constraintBottom_toTopOf="@+id/area"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintHorizontal_bias="1.0"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toBottomOf="@+id/num2"
    tools:ignore="SpeakableTextPresentCheck,TouchTargetSizeCheck" />

<Button
    android:id="@+id/area"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginStart="48dp"
    android:layout_marginTop="12dp"
    android:layout_marginEnd="269dp"
    android:layout_marginBottom="314dp"
    android:text="area"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintHorizontal_bias="1.0"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toBottomOf="@+id/num3" />

<Button
    android:id="@+id/perimeter"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginStart="224dp"
    android:layout_marginTop="4dp"
    android:layout_marginEnd="93dp"
    android:layout_marginBottom="50dp"
    android:text="perimeter"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintHorizontal_bias="1.0"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toBottomOf="@+id/num3"
    app:layout_constraintVertical_bias="0.17" />

<TextView
    android:id="@+id/ans"
    android:layout_width="156dp"
    android:layout_height="58dp"
    android:layout_marginStart="114dp"
    android:layout_marginTop="68dp"
    android:layout_marginEnd="135dp"
    android:layout_marginBottom="184dp"
    android:text="TextView"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintHorizontal_bias="1.0"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toBottomOf="@+id/area"
    app:layout_constraintVertical_bias="1.0" />

</androidx.constraintlayout.widget.ConstraintLayout>

Main_activity.java
package com.example.triangle;

import androidx.appcompat.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 n1,n2,n3;
private TextView t1;
private Button b1,b2;
Double side1,side2,side3,area1,perimeter1;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    n1 =(EditText) findViewById(R.id.num1);
    n2 =(EditText)  findViewById(R.id.num2);
    n3 =(EditText) findViewById(R.id.num3);

    t1 = (TextView) findViewById(R.id.ans);
    b1 = (Button) findViewById(R.id.area);
    b2 = (Button) findViewById(R.id.perimeter);

    b1.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            side1 = Double.parseDouble(n1.getText().toString());
            side2 = Double.parseDouble(n2.getText().toString());
            /* area = 0.5 * base * height*/
            area1 = 0.5*side1*side2;
            t1.setText("Area : "+area1);
        }
    });

    b2.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            side1 = Double.parseDouble(n1.getText().toString());
            side2 = Double.parseDouble(n2.getText().toString());
            side3 = Double.parseDouble(n3.getText().toString());
            /*perimeter = side+side+base*/
            perimeter1 = side1+side2+side3;
            t1.setText("Perimeter : "+perimeter1);


        }
    });




}

}