获取java.lang.StringIndexOutOfBoundsException

Question

Disclaimer: I'm a beginner straight out of AP Computer Science.

I'm trying to make an app that converts text input from the user into pig latin, for practice. It's a work in progress but so far i'm getting exceptions.

Here's my code:

package com.example.ashavolian.piglatin2;

import android.content.DialogInterface;
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;
import android.view.View.OnClickListener;

public class MainActivity extends AppCompatActivity {

    TextView txtOut;
    EditText txtIn;
    Button button;

    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        txtOut = (TextView) findViewById(R.id.txtOut);
        txtIn = (EditText) findViewById(R.id.txtIn);
        button = (Button) findViewById(R.id.button);

        button.setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View v) {
                String txtTxtIn = txtIn.getText().toString();
                txtOut.setText(translate(txtTxtIn));
            }
        });

    }

    public String translate(String txtTxtIn)
    {
        txtTxtIn += " "; 
        int length = txtTxtIn.length();
        String pigLatin = " ";

        for (int b = 0; b < length; b++) {
            int space = txtTxtIn.indexOf(" ");
            String word = txtTxtIn.substring(0, space);
            int a = word.indexOf("a");
            int e = word.indexOf("e");
            int i = word.indexOf("i");
            int o = word.indexOf("o");
            int u = word.indexOf("u");

            int vowels[] = {a, e, i, o, u};

            for (int c = 0; c < 4; c++)
            {
                if (vowels[c] == -1)
                    vowels[c] += 101;
            }

            for (int d = 0; d < 4; d++)
            {
                if (vowels[d] > -1 && vowels[d] <= vowels[0] && vowels[d] <= vowels[1] && vowels[d] <= vowels[2] && vowels[d] <= vowels[3] && vowels[d] <= vowels[4])
                {
                    word = word.substring(vowels[i] + 1) + word.substring(0,vowels[i]);
                    pigLatin += " " + word;
                }
            }
            txtTxtIn = txtTxtIn.substring(space + 1);
        }

        return pigLatin;
    }

}

The exception only occurs when you press the button. Making the Program crash.

Here's the exception:

FATAL EXCEPTION: main
Process: com.example.ashavolian.piglatin2, PID: 2991
java.lang.StringIndexOutOfBoundsException: length=0; regionStart=0; regionLength=-1
    at java.lang.String.startEndAndLength(String.java:298)
    at java.lang.String.substring(String.java:1087)
    at com.example.ashavolian.piglatin2.MainActivity.translate(MainActivity.java:39)
    at com.example.ashavolian.piglatin2.MainActivity$1.onClick(MainActivity.java:27)
    at android.view.View.performClick(View.java:5198)
    at android.view.View$PerformClick.run(View.java:21147)
    at android.os.Handler.handleCallback(Handler.java:739)
    at android.os.Handler.dispatchMessage(Handler.java:95)
    at android.os.Looper.loop(Looper.java:148)
    at android.app.ActivityThread.main(ActivityThread.java:5417)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

Answer 1

I suppose, an exception is thrown when you try to access element in the array with an index, which doesn't actually exist. It's typical situation, when you get IndexOutOfBoundsException or StringIndexOutOfBoundsException .

I cannot tell you in which line is a real mistake without debugging the application. Your translate(String) method is doing strange stuff and code is not so clean. Nevertheless, I have the following candidates, which could cause that exception:

• vowels[i] - i variable is calculated by int i = word.indexOf("i"); and word is calculated by txtTxtIn.substring(0, space); , but you cannot be sure about length of txtxTxtIn , but max index of vovels is 4. When txtTxtIn has more characters than 5, an exception will be thrown
• txtTxtIn = txtTxtIn.substring(space + 1); - here may be similar story as above

My suggestion is to debug this code. Moreover, you could use List . It's Java and we have such structures here. It would be much easier to perform operations on strings and chars and harder to make such mistake.

Answer 2

Variable i in the following code is the problem.

word = word.substring(vowels[i] + 1) + word.substring(0,vowels[i]);

Check whether you want the variable i or some other variable.