如果我对其他活动的所有内容都进行评论，程序就会运行，但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);
}
我创建了一个我想要使用的类的Object：
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logcat
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，所以我不擅长调试，所以有人可以帮助我解决困境吗？
答案 0 :(得分：3)
除了实例化一个活动是你在android中无法做到的事情（@Gabe回答），
您的问题的基本Java原因是您有一个班级Calculator和一个班级Settings extends Calculator，并且您在Settings的初始版中创建了一个新的Calculator。
创建新的Calculator活动时，会创建新的Settings活动。此类扩展Calculator，因此继承init和字段。
因此，创建新的Settings会调用Calculator的init，这会创建一个新的Settings，依此类推。
这是导致堆栈溢出的原因。