java - 通过另一个类使用 setter 时发生堆栈溢出异常

Question

如果我注释掉与其他 Activity 有关的所有内容，程序就会运行，但是当我尝试使用它运行我的程序时，它会在遇到此行时立即崩溃:

    if(savedInstanceState == null)
    {
        settings.setImperial(true);
        settings.setUK(true);
    }

我已经创建了一个我希望使用的类的对象:

private FuelEconomySettingsActivity settings = new FuelEconomySettingsActivity();

这是FuelEconomyCalculatorActivity.java

package com.example.fuelcalculator;

import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.ActionBarActivity;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.RadioButton;
import android.widget.TextView;
import android.widget.Toast;

public class FuelEconomyCalculatorActivity extends ActionBarActivity implements
        OnClickListener {

    private EditText fuelEditText;
    private EditText distanceEditText;
    private TextView mpgTextView;
    private TextView litresTextView;
    private Button calculateButton;
    private Button clearButton;
    private RadioButton gallonsRadio;
    private RadioButton litresRadio;
    private RadioButton milesRadio;
    private RadioButton kmRadio;
    private String mpg = " ";
    private String kp100 = " ";

    private FuelEconomySettingsActivity settings = new FuelEconomySettingsActivity();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_fuel_economy_calculator);
        fuelEditText = (EditText) findViewById(R.id.fuelEditText);
        distanceEditText = (EditText) findViewById(R.id.distanceEditText);
        mpgTextView = (TextView) findViewById(R.id.mpgTextView);
        litresTextView = (TextView) findViewById(R.id.litresTextView);
        calculateButton = (Button) findViewById(R.id.calculateButton);
        clearButton = (Button) findViewById(R.id.clearButton);
        gallonsRadio = (RadioButton) findViewById(R.id.gallonsRadio);
        litresRadio = (RadioButton) findViewById(R.id.litresRadio);
        milesRadio = (RadioButton) findViewById(R.id.milesRadio);
        kmRadio = (RadioButton) findViewById(R.id.kmRadio);
        calculateButton.setOnClickListener(this);
        clearButton.setOnClickListener(this);

        litresRadio.setChecked(true);
        kmRadio.setChecked(true);

        if(savedInstanceState == null)
        {
            settings.setImperial(true);
            settings.setUK(true);
        }

        if (settings.getImperial()) {
            litresRadio.setChecked(true);
            kmRadio.setChecked(true);
        } else if (settings.getMetric()) {
            gallonsRadio.setChecked(true);
            milesRadio.setChecked(true);
        }

        if (savedInstanceState != null) {
            mpg = savedInstanceState.getString("mpg");
            kp100 = savedInstanceState.getString("kp100");
        }
        initializeViews();
    }

    protected void onSaveInstanceState(Bundle savedInstanceState) {
        super.onSaveInstanceState(savedInstanceState);
        savedInstanceState.putString("mpg", (String) mpgTextView.getText());
        savedInstanceState.putString("kp100", (String) litresTextView.getText());
    }

    private void initializeViews() {
        mpgTextView.setText(mpg);
        litresTextView.setText(kp100);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.fuel_economy_calculator, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        switch (item.getItemId()) {
        case R.id.action_settings: {
            Intent intent = new Intent(FuelEconomyCalculatorActivity.this,
                    FuelEconomySettingsActivity.class);
            startActivity(intent);
            return true;
        }

        case R.id.action_about: {
            Intent intent = new Intent(FuelEconomyCalculatorActivity.this,
                    FuelEconomyAboutPageActivity.class);
            startActivity(intent);
            return true;
        }

        default:
            return super.onOptionsItemSelected(item);
        }
    }

    @Override
    public void onClick(View v) {
        if (v.getId() == R.id.calculateButton) {
            float mpg = 0;
            float kmLitres = 0;
            // it doesn't matter which you use here, as long
            // as you use a fuel and a distance method
            if (settings.getUK() && !settings.getUS()) {
                if (getKM() > 0 && getLitres() > 0) {
                    mpg = getMiles() / getGallons();
                    kmLitres = getLitres() / (getKM() / 100);
                    mpgTextView.setText(String.format("%.2f", mpg));
                    litresTextView.setText(String.format("%.2f", kmLitres));
                }
            } else if (settings.getUS() && !settings.getUK()) {
                if (getKM() > 0 && getLitres() > 0) {
                    mpg = getMiles() / getGallonsUS();
                    kmLitres = getLitresUS() / (getKM() / 100);
                    mpgTextView.setText(String.format("%.2f", mpg));
                    litresTextView.setText(String.format("%.2f", kmLitres));
                }
            }
        } else if (v.getId() == R.id.clearButton) {
            resetValues();
        }

    }

    public float CheckValues(EditText input) {
        float value = 0;
        try {
            value = Float.parseFloat(input.getText().toString());
            if (value < 1) {
                Toast toast = Toast.makeText(this,
                        "Please enter a number that is larger than 0",
                        Toast.LENGTH_SHORT);
                toast.show();
            }
        } catch (Exception ex) {
            Toast toast = Toast.makeText(this, "Please enter a number",
                    Toast.LENGTH_SHORT);
            toast.show();
        }
        return value;
    }

    public void resetValues() {
        mpg = " ";
        kp100 = " ";
        fuelEditText.setText("");
        distanceEditText.setText("");
        mpgTextView.setText("");
        litresTextView.setText("");
    }

    public float getKM() {
        float distance = CheckValues(distanceEditText);
        if (milesRadio.isChecked()) {
            distance = (float) (distance * 1.60934);
        }
        return distance;
    }

    public float getMiles() {
        float distance = CheckValues(distanceEditText);
        if (kmRadio.isChecked()) {
            distance = (float) (distance * 0.62137);
        }
        return distance;
    }

    public float getLitres() {
        float fuel = CheckValues(fuelEditText);
        if (gallonsRadio.isChecked()) {
            fuel = (float) (fuel * 4.54609);
        }
        return fuel;
    }

    public float getLitresUS() {
        float fuel = CheckValues(fuelEditText);
        if (gallonsRadio.isChecked()) {
            fuel = (float) (fuel * 3.785411784);
        }
        return fuel;
    }

    public float getGallons() {
        float fuel = CheckValues(fuelEditText);
        if (litresRadio.isChecked()) {
            fuel = (float) (fuel * 0.219969);
        }
        return fuel;
    }

    public float getGallonsUS() {
        float fuel = CheckValues(fuelEditText);
        if (litresRadio.isChecked()) {
            fuel = (float) (fuel * 0.264172);
        }
        return fuel;
    }
}

这是我的FuelEconomySettingsActivity.java

package com.example.fuelcalculator;

import android.content.Intent;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.RadioButton;

public class FuelEconomySettingsActivity extends FuelEconomyCalculatorActivity {

    private RadioButton metricRadio;
    private RadioButton imperialRadio;
    private RadioButton usRadio;
    private RadioButton ukRadio;

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

        metricRadio = (RadioButton) findViewById(R.id.metricRadioText);
        imperialRadio = (RadioButton) findViewById(R.id.imperialRadioText);
        usRadio = (RadioButton) findViewById(R.id.usRadioText);
        ukRadio = (RadioButton) findViewById(R.id.ukRadioText);

        imperialRadio.setChecked(true);
        ukRadio.setChecked(true);

    }

    public void setMetric(boolean b) {
        metricRadio.setChecked(b);
    }

    public void setImperial(boolean b) {
        imperialRadio.setChecked(b);
    }

    public void setUS(boolean b) {
        usRadio.setChecked(b);
    }

    public void setUK(boolean b) {
        ukRadio.setChecked(b);
    }   

    public boolean getMetric() {
        if (metricRadio.isChecked())
            return true;
        else
            return false;
    }

    public boolean getImperial() {
        if (imperialRadio.isChecked())
            return true;
        else
            return false;
    }

    public boolean getUS() {
        if (usRadio.isChecked())
            return true;
        else
            return false;
    }

    public boolean getUK() {
        if (ukRadio.isChecked())
            return true;
        else
            return false;
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.fuel_economy_calculator, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        switch (item.getItemId()) {
        case R.id.action_about: {
            Intent intent = new Intent(FuelEconomySettingsActivity.this,
                    FuelEconomyAboutPageActivity.class);
            startActivity(intent);
            return true;
        }

        case R.id.action_main: {
            Intent intent = new Intent(FuelEconomySettingsActivity.this,
                    FuelEconomyCalculatorActivity.class);
            startActivity(intent);
            return true;
        }

        default:
            return super.onOptionsItemSelected(item);
        }
    }
}

这是日志

07-17 16:04:44.868: E/AndroidRuntime(31697): FATAL EXCEPTION: main
07-17 16:04:44.868: E/AndroidRuntime(31697): Process: com.example.fuelcalculator, PID: 31697
07-17 16:04:44.868: E/AndroidRuntime(31697): java.lang.StackOverflowError
07-17 16:04:44.868: E/AndroidRuntime(31697):    at java.lang.ref.FinalizerReference.add(FinalizerReference.java:54)
07-17 16:04:44.868: E/AndroidRuntime(31697):    at android.os.StrictMode$InstanceTracker.<init>(StrictMode.java:2255)
07-17 16:04:44.868: E/AndroidRuntime(31697):    at android.os.StrictMode.trackActivity(StrictMode.java:1957)
07-17 16:04:44.868: E/AndroidRuntime(31697):    at android.app.Activity.<init>(Activity.java:779)
07-17 16:04:44.868: E/AndroidRuntime(31697):    at android.support.v4.app.FragmentActivity.<init>(FragmentActivity.java:76)
07-17 16:04:44.868: E/AndroidRuntime(31697):    at android.support.v7.app.ActionBarActivity.<init>(ActionBarActivity.java:55)
07-17 16:04:44.868: E/AndroidRuntime(31697):    at com.example.fuelcalculator.FuelEconomyCalculatorActivity.<init>(FuelEconomyCalculatorActivity.java:16)
07-17 16:04:44.868: E/AndroidRuntime(31697):    at com.example.fuelcalculator.FuelEconomySettingsActivity.<init>(FuelEconomySettingsActivity.java:9)
07-17 16:04:44.868: E/AndroidRuntime(31697):    at com.example.fuelcalculator.FuelEconomyCalculatorActivity.<init>(FuelEconomyCalculatorActivity.java:32)
07-17 16:04:44.868: E/AndroidRuntime(31697):    at com.example.fuelcalculator.FuelEconomySettingsActivity.<init>(FuelEconomySettingsActivity.java:9)
07-17 16:04:44.868: E/AndroidRuntime(31697):    at com.example.fuelcalculator.FuelEconomyCalculatorActivity.<init>(FuelEconomyCalculatorActivity.java:32)
07-17 16:04:44.868: E/AndroidRuntime(31697):    at com.example.fuelcalculator.FuelEconomySettingsActivity.<init>(FuelEconomySettingsActivity.java:9)
07-17 16:04:44.868: E/AndroidRuntime(31697):    at com.example.fuelcalculator.FuelEconomyCalculatorActivity.<init>(FuelEconomyCalculatorActivity.java:32)
07-17 16:04:44.868: E/AndroidRuntime(31697):    at com.example.fuelcalculator.FuelEconomySettingsActivity.<init>(FuelEconomySettingsActivity.java:9)
07-17 16:04:44.868: E/AndroidRuntime(31697):    at com.example.fuelcalculator.FuelEconomyCalculatorActivity.<init>(FuelEconomyCalculatorActivity.java:32)
07-17 16:04:44.868: E/AndroidRuntime(31697):    at com.example.fuelcalculator.FuelEconomySettingsActivity.<init>(FuelEconomySettingsActivity.java:9)
07-17 16:04:44.868: E/AndroidRuntime(31697):    at com.example.fuelcalculator.FuelEconomyCalculatorActivity.<init>(FuelEconomyCalculatorActivity.java:32)
07-17 16:04:44.868: E/AndroidRuntime(31697):    at com.example.fuelcalculator.FuelEconomySettingsActivity.<init>(FuelEconomySettingsActivity.java:9)
07-17 16:04:44.868: E/AndroidRuntime(31697):    at com.example.fuelcalculator.FuelEconomyCalculatorActivity.<init>(FuelEconomyCalculatorActivity.java:32)
07-17 16:04:44.868: E/AndroidRuntime(31697):    at com.example.fuelcalculator.FuelEconomySettingsActivity.<init>(FuelEconomySettingsActivity.java:9)
07-17 16:04:44.868: E/AndroidRuntime(31697):    at com.example.fuelcalculator.FuelEconomyCalculatorActivity.<init>(FuelEconomyCalculatorActivity.java:32)
07-17 16:04:44.868: E/AndroidRuntime(31697):    at com.example.fuelcalculator.FuelEconomySettingsActivity.<init>(FuelEconomySettingsActivity.java:9)
07-17 16:04:44.868: E/AndroidRuntime(31697):    at com.example.fuelcalculator.FuelEconomyCalculatorActivity.<init>(FuelEconomyCalculatorActivity.java:32)
07-17 16:04:44.868: E/AndroidRuntime(31697):    at com.example.fuelcalculator.FuelEconomySettingsActivity.<init>(FuelEconomySettingsActivity.java:9)
07-17 16:04:44.868: E/AndroidRuntime(31697):    at com.example.fuelcalculator.FuelEconomyCalculatorActivity.<init>(FuelEconomyCalculatorActivity.java:32)
07-17 16:04:44.868: E/AndroidRuntime(31697):    at com.example.fuelcalculator.FuelEconomySettingsActivity.<init>(FuelEconomySettingsActivity.java:9)
07-17 16:04:44.868: E/AndroidRuntime(31697):    at com.example.fuelcalculator.FuelEconomyCalculatorActivity.<init>(FuelEconomyCalculatorActivity.java:32)
07-17 16:04:44.868: E/AndroidRuntime(31697):    at com.example.fuelcalculator.FuelEconomySettingsActivity.<init>(FuelEconomySettingsActivity.java:9)
07-17 16:04:44.868: E/AndroidRuntime(31697):    at com.example.fuelcalculator.FuelEconomyCalculatorActivity.<init>(FuelEconomyCalculatorActivity.java:32)
07-17 16:04:44.868: E/AndroidRuntime(31697):    at com.example.fuelcalculator.FuelEconomySettingsActivity.<init>(FuelEconomySettingsActivity.java:9)
07-17 16:04:44.868: E/AndroidRuntime(31697):    at com.example.fuelcalculator.FuelEconomyCalculatorActivity.<init>(FuelEconomyCalculatorActivity.java:32)
07-17 16:04:44.868: E/AndroidRuntime(31697):    at com.example.fuelcalculator.FuelEconomySettingsActivity.<init>(FuelEconomySettingsActivity.java:9)
07-17 16:04:44.868: E/AndroidRuntime(31697):    at com.example.fuelcalculator.FuelEconomyCalculatorActivity.<init>(FuelEconomyCalculatorActivity.java:32)
07-17 16:04:44.868: E/AndroidRuntime(31697):    at com.example.fuelcalculator.FuelEconomySettingsActivity.<init>(FuelEconomySettingsActivity.java:9)
07-17 16:04:44.868: E/AndroidRuntime(31697):    at com.example.fuelcalculator.FuelEconomyCalculatorActivity.<init>(FuelEconomyCalculatorActivity.java:32)
07-17 16:04:44.868: E/AndroidRuntime(31697):    at com.example.fuelcalculator.FuelEconomySettingsActivity.<init>(FuelEconomySettingsActivity.java:9)
07-17 16:04:44.868: E/AndroidRuntime(31697):    at com.example.fuelcalculator.FuelEconomyCalculatorActivity.<init>(FuelEconomyCalculatorActivity.java:32)
07-17 16:04:44.868: E/AndroidRuntime(31697):    at com.example.fuelcalculator.FuelEconomySettingsActivity.<init>(FuelEconomySettingsActivity.java:9)
07-17 16:04:44.868: E/AndroidRuntime(31697):    at com.example.fuelcalculator.FuelEconomyCalculatorActivity.<init>(FuelEconomyCalculatorActivity.java:32)
07-17 16:04:44.868: E/AndroidRuntime(31697):    at com.example.fuelcalculator.FuelEconomySettingsActivity.<init>(FuelEconomySettingsActivity.java:9

我是 Android 的新手，所以我不太擅长调试，所以有人可以帮助我解决我的困境吗？

Answer 1

除了实例化一个 Activity 是你在 android 中不能真正做到的事情(@Gabe 回答)之外，

您的问题的根本 Java 原因是您有一个类 Calculator 和一个类 Settings extends Calculator，并且您创建了一个新的 Settings 在 Calculator 的初始化中。

当您创建一个新的Calculator Activity 时，会创建一个新的Settings Activity 。此类扩展 Calculator，因此继承了 init 和字段。

因此，创建一个新的 Settings 会调用 Calculator 的 init，它会为自己创建一个新的 Settings，依此类推。

这就是导致堆栈溢出的原因。