I'm getting java.lang.StringIndexOutOfBoundsException: String index out of range: -1

oussama Published at Dev

Oussama

Hello guys i'm new to android development and i'm currently trying to build a simple a calculator however when i click the c button it just turns the last character to a "C" Here's the line of code i used:

if (buttonText.equals("C")) {
            dataToCalculate = dataToCalculate.substring(0,dataToCalculate.length()-1);
        }

and Here's the full code:

package com.example.icalculate;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.view.View;
import android.widget.TextView;

import com.google.android.material.button.MaterialButton;

import org.w3c.dom.Text;

public class MainActivity extends AppCompatActivity implements View.OnClickListener{
    private TextView textResult, textSolution;
    private MaterialButton btnC,btnOpenBracket,btnClosedBracket,btnDivide;
    private MaterialButton btn7,btn8,btn9,btnMultiply;
    private MaterialButton btn4,btn5,btn6,btnPlus;
    private MaterialButton btn1,btn2,btn3,btnMinus;
    private MaterialButton btnAC,btn0,btnDot,btnEquals;

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

        textResult = (TextView) findViewById(R.id.txtResult);
        textSolution = (TextView) findViewById(R.id.txtSolution);

        assignId(btnC, R.id.button_c);
        assignId(btnOpenBracket, R.id.button_open_bracket);
        assignId(btnClosedBracket, R.id.button_closed_bracket);
        assignId(btnDivide, R.id.button_divide);
        assignId(btn7, R.id.button_7);
        assignId(btn8, R.id.button_8);
        assignId(btn9, R.id.button_9);
        assignId(btnMultiply, R.id.button_multiply);
        assignId(btn4, R.id.button_4);
        assignId(btn5, R.id.button_5);
        assignId(btn6, R.id.button_6);
        assignId(btnPlus, R.id.button_plus);
        assignId(btn1, R.id.button_1);
        assignId(btn2, R.id.button_2);
        assignId(btn3, R.id.button_3);
        assignId(btnMinus, R.id.button_minus);
        assignId(btnAC, R.id.button_ac);
        assignId(btn0, R.id.button_0);
        assignId(btnDot, R.id.button_dot);
        assignId(btnEquals, R.id.button_equals);
    }

    void assignId(MaterialButton btn, int id) {
        btn = findViewById(id);
        btn.setOnClickListener(this);

    }

    @Override
    public void onClick(View v) {
        MaterialButton button = (MaterialButton) v;
        String buttonText = button.getText().toString();
        String dataToCalculate = textSolution.getText().toString();

        if (buttonText.equals("AC")) {
            textSolution.setText("");
            textResult.setText("0");
            return;
        }
        if (buttonText.equals("C")) {
            dataToCalculate = dataToCalculate.substring(0,dataToCalculate.length()-1);
        }
        if (buttonText.equals("=")) {
            textSolution.setText(textResult.getText());
        }else {
            dataToCalculate = dataToCalculate+buttonText;
        }
        textSolution.setText(dataToCalculate);

    }
}

Reilas

There is more than one situation here.

Firstly, if you're encountering a StringIndexOutOfBoundsException, then it would mean dataToCalculate has a length of 0.
Because, dataToCalculate.length() - 1, on a length of 0, will return −1.

You can remedy this by checking the length first—I typically use String#isEmpty.

if (!dataToCalculate.isEmpty()) {
    dataToCalculate = dataToCalculate.substring(0,dataToCalculate.length()-1);
}

Furthermore, you can simplify your code to the following.

switch (buttonText) {
    case "AC" -> {
        textSolution.setText("");
        textResult.setText("0");
        return;
    }
    case "C" -> {
        if (!dataToCalculate.isEmpty())
            dataToCalculate = dataToCalculate.substring(0, dataToCalculate.length() - 1);
    }
    case "=" -> textSolution.setText(textResult.getText());
    default -> dataToCalculate = dataToCalculate+buttonText;
}
textSolution.setText(dataToCalculate);

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