Calculator (Java)

/*
Inside build.gradle -> implementation
implementation 'com.faendir.rhino:rhino-android:1.5.2'
*/

package com.example.calculator;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.util.Log;
import android.util.TypedValue;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

import org.mozilla.javascript.Context;
import org.mozilla.javascript.Scriptable;

public class MainActivity extends AppCompatActivity {

    Button btn0, btn1, btn2, btn3, btn4, btn5, btn6, btn7, btn8, btn9, btnAdd, btnSubtract, btnMultiply, btnDivision, btnMod, btnParenthesis, btnEqual, btnDot, btnClear, btnPecentage;

    TextView output, input;

    boolean startPar = false;

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

        btn0 = findViewById(R.id.btn0);
        btn1 = findViewById(R.id.btn1);
        btn2 = findViewById(R.id.btn2);
        btn3 = findViewById(R.id.btn3);
        btn4 = findViewById(R.id.btn4);
        btn5 = findViewById(R.id.btn5);
        btn6 = findViewById(R.id.btn6);
        btn7 = findViewById(R.id.btn7);
        btn8 = findViewById(R.id.btn8);
        btn9 = findViewById(R.id.btn9);
        btnAdd = findViewById(R.id.btnAdd);
        btnSubtract = findViewById(R.id.btnSubtract);
        btnMultiply = findViewById(R.id.btnMultiply);
        btnDivision = findViewById(R.id.btnDivision);
        btnMod = findViewById(R.id.btnMod);
        btnDot = findViewById(R.id.btnDot);
        btnParenthesis = findViewById(R.id.btnParenthesis);
        btnPecentage = findViewById(R.id.btnPercentage);
        btnClear = findViewById(R.id.btnClear);
        btnEqual = findViewById(R.id.btnEqual);

        input = findViewById(R.id.input);
        output = findViewById(R.id.output);


        btnClear.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                input.setText("");
                output.setText("");
                startPar = false;
                input.setTextSize(TypedValue.COMPLEX_UNIT_SP, 60);
            }
        });

        btn0.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String text = input.getText().toString();
                input.setText(text+"0");
            }
        });

        btn1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String text = input.getText().toString();
                input.setText(text+"1");
            }
        });

        btn2.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String text = input.getText().toString();
                input.setText(text+"2");
            }
        });

        btn3.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String text = input.getText().toString();
                input.setText(text+"3");
            }
        });

        btn4.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String text = input.getText().toString();
                input.setText(text+"4");
            }
        });

        btn5.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String text = input.getText().toString();
                input.setText(text+"5");
            }
        });

        btn6.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String text = input.getText().toString();
                input.setText(text+"6");
            }
        });


        btn7.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String text = input.getText().toString();
                input.setText(text+"7");
            }
        });

        btn8.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String text = input.getText().toString();
                input.setText(text+"8");
            }
        });

        btn9.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String text = input.getText().toString();
                input.setText(text+"9");
            }
        });

        btnAdd.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String text = input.getText().toString();
                input.setText(text+"+");
            }
        });

        btnSubtract.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String text = input.getText().toString();
                input.setText(text+"−");
            }
        });

        btnMultiply.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String text = input.getText().toString();
                input.setText(text+"×");
            }
        });

        btnDivision.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String text = input.getText().toString();
                input.setText(text+"÷");
            }
        });

        btnPecentage.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String text = input.getText().toString();
                input.setText(text+"%");
            }
        });

        btnDot.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String text = input.getText().toString();
                input.setText(text+".");
            }
        });

        btnMod.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String text = input.getText().toString();
                input.setText(text+"Mod");
            }
        });

        btnParenthesis.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String text = input.getText().toString();
                if (startPar)
                    input.setText(text + ")");
                else
                    input.setText(text+"(");

                startPar = !startPar;
            }
        });

        btnEqual.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String text = input.getText().toString();

                if ("".equals(text)) {
                    startPar = false;
                    return;
                }

                output.setText(text);

                text = text.replaceAll("÷", "/");
                text = text.replaceAll("%", "/100");
                text = text.replaceAll("×", "*");
                text = text.replaceAll("−", "-");
                text = text.replaceAll("Mod", "%");

                org.mozilla.javascript.Context rhino = Context.enter();

                rhino.setOptimizationLevel(-1);


                String result = "";

                try {
                    Scriptable scriptable = rhino.initStandardObjects();
                    result = rhino.evaluateString(scriptable, text, "javascript", 1, null).toString();
                }
                catch (Exception e) {
                    result = "0";
                }

                if (result.length() > 10) {
                    input.setTextSize(TypedValue.COMPLEX_UNIT_SP, 37);
                }

                input.setText(result);
                startPar = false;
            }
        });
    }
}