Calculator Example in Android

MainActivity.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.practice.bhaumik.calculator.MainActivity">

    <TextView
        android:layout_width="match_parent"
        android:layout_height="70sp"
        android:textSize="50sp"
        android:textAlignment="textEnd"
        android:id="@+id/tv_input"
        />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="80sp"
        android:text="7"
        android:textSize="25sp"
        android:id="@+id/btn7"
        android:minHeight="60sp"/>
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="80sp"
        android:text="8"
        android:textSize="25sp"
        android:id="@+id/btn8"
        android:minHeight="60sp"
        android:layout_toRightOf="@+id/btn7"/>
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="80sp"
        android:text="9"
        android:textSize="25sp"
        android:id="@+id/btn9"
        android:minHeight="60sp"
        android:layout_toRightOf="@+id/btn8"/>
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="80sp"
        android:text="Del"
        android:textSize="18sp"
        android:minHeight="60sp"
        android:id="@+id/btn_del"
        android:layout_toRightOf="@+id/btn9"/>
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="150sp"
        android:text="4"
        android:textSize="25sp"
        android:minHeight="60sp"
        android:id="@+id/btn4"
        />
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="150sp"
        android:text="5"
        android:textSize="25sp"
        android:minHeight="60sp"
        android:id="@+id/btn5"
        android:layout_toRightOf="@+id/btn4"
        />
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="150sp"
        android:text="6"
        android:textSize="25sp"
        android:minHeight="60sp"
        android:id="@+id/btn6"
        android:layout_toRightOf="@+id/btn5"
        />
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="150sp"
        android:text="/"
        android:textSize="22sp"
        android:minHeight="60sp"
        android:id="@+id/btn_divide"
        android:layout_toRightOf="@+id/btn6"
        />
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="220sp"
        android:text="1"
        android:textSize="22sp"
        android:minHeight="60sp"
        android:id="@+id/btn1"
        />
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="220sp"
        android:text="2"
        android:textSize="22sp"
        android:minHeight="60sp"
        android:id="@+id/btn2"
        android:layout_toRightOf="@+id/btn1"
        />
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="220sp"
        android:text="3"
        android:textSize="22sp"
        android:minHeight="60sp"
        android:id="@+id/btn3"
        android:layout_toRightOf="@+id/btn2"
        />
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="220sp"
        android:text="X"
        android:textSize="22sp"
        android:minHeight="60sp"
        android:id="@+id/btn_multiply"
        android:layout_toRightOf="@+id/btn3"
        />
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="290sp"
        android:text="."
        android:textSize="22sp"
        android:minHeight="60sp"
        android:id="@+id/btn_dot"
        />
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="290sp"
        android:text="0"
        android:textSize="22sp"
        android:minHeight="60sp"
        android:id="@+id/btn0"
        android:layout_toRightOf="@+id/btn_dot"
        />
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="290sp"
        android:text="="
        android:textSize="22sp"
        android:minHeight="60sp"
        android:id="@+id/btn_equal"
        android:layout_toRightOf="@+id/btn0"
        />
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="290sp"
        android:text="+"
        android:textSize="22sp"
        android:minHeight="60sp"
        android:id="@+id/btn_plus"
        android:layout_toRightOf="@+id/btn_equal"
        />
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="360sp"
        android:text="-"
        android:textSize="22sp"
        android:minHeight="60sp"
        android:id="@+id/btn_minus"
        android:layout_toRightOf="@+id/btn_equal"
        />
</RelativeLayout>

MainActivity.java

package com.practice.bhaumik.calculator;

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

public class MainActivity extends AppCompatActivity {

    float num1 = 0,num2 = 0;

    TextView textView;
    Button b1,b2,b3,b4,b5,b6,b7,b8,b9,b0,dot,equal,plus,minus,mul,div,del;
    boolean add,sub,multi,division;

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

        textView = (TextView) findViewById(R.id.tv_input);
        b1 = (Button) findViewById(R.id.btn1);
        b2 = (Button) findViewById(R.id.btn2);
        b3 = (Button) findViewById(R.id.btn3);
        b4 = (Button) findViewById(R.id.btn4);
        b5 = (Button) findViewById(R.id.btn5);
        b6 = (Button) findViewById(R.id.btn6);
        b7 = (Button) findViewById(R.id.btn7);
        b8 = (Button) findViewById(R.id.btn8);
        b9 = (Button) findViewById(R.id.btn9);
        b0 = (Button) findViewById(R.id.btn0);
        equal = (Button) findViewById(R.id.btn_equal);
        plus = (Button) findViewById(R.id.btn_plus);
        minus = (Button) findViewById(R.id.btn_minus);
        mul = (Button) findViewById(R.id.btn_multiply);
        div = (Button) findViewById(R.id.btn_divide);
        del = (Button) findViewById(R.id.btn_del);
        dot = (Button) findViewById(R.id.btn_dot);
        b1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                textView.setText(textView.getText() + "1");
            }
        });
        b2.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                textView.setText(textView.getText() + "2");
            }
        });
        b3.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                textView.setText(textView.getText() + "3");
            }
        });
        b4.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                textView.setText(textView.getText() + "4");
            }
        });
        b5.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                textView.setText(textView.getText() + "5");
            }
        });
        b6.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                textView.setText(textView.getText() + "6");
            }
        });
        b7.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                textView.setText(textView.getText() + "7");
            }
        });
        b8.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                textView.setText(textView.getText() + "8");
            }
        });
        b9.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                textView.setText(textView.getText() + "9");
            }
        });
        b0.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                textView.setText(textView.getText() + "0");
            }
        });
        dot.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                textView.setText(textView.getText() + ".");
            }
        });
        plus.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                num1 = Float.parseFloat(textView.getText() + "");

                add = true;
                textView.setText("");
            }
        });
        minus.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                num1 = Float.parseFloat(textView.getText() + "");
                sub = true;
                textView.setText("");
            }
        });
        mul.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                num1 = Float.parseFloat(textView.getText() + "");
                multi = true;
                textView.setText("");
            }
        });
        div.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                num1 = Float.parseFloat(textView.getText() + "");
                division = true;
                textView.setText("");
            }
        });
        del.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                textView.setText("");
            }
        });
        equal.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                num2 = Float.parseFloat(textView.getText() + "");

                if(add == true)
                {
                    textView.setText(String.valueOf(num1 + num2));
                    add = false;
                }
                if(sub == true)
                {
                    textView.setText(String.valueOf(num1 - num2));
                    sub = false;
                }
                if(multi == true)
                {
                    textView.setText(String.valueOf(num1 * num2));
                    multi = false;
                }
                if(division == true)
                {
                    textView.setText(String.valueOf(num1 / num2));
                    division = false;
                }
            }
        });
    }

}