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起初我對我的壞英語感到抱歉。致命例外：主[Android開發]
的問題：我編譯這段代碼（MyActivity.java）：
package com.bundas.tdsestr.kalkulacka;
import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.*;
public class MyActivity extends Activity {
private int[] array = new int[19999];
private String[] text_na_displeji = new String[19999];
private int postup = 0;
private TextView Display;
private Button tlacitko1, tlacitko2, tlacitko3, tlacitko4, tlacitko5, tlacitko6, tlacitko7, tlacitko8, tlacitko9, rovnaSe, plus, minus;
public String vysledek = "";
private int konecnyVysledek=0;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_my);
this.tlacitko1 = (Button)findViewById(R.id.tlacitko1);
this.tlacitko2 = (Button)findViewById(R.id.tlacitko2);
this.tlacitko3 = (Button)findViewById(R.id.tlacitko3);
this.tlacitko4 = (Button)findViewById(R.id.tlacitko4);
this.tlacitko5 = (Button)findViewById(R.id.tlacitko5);
this.tlacitko6 = (Button)findViewById(R.id.tlacitko6);
this.tlacitko7 = (Button)findViewById(R.id.tlacitko7);
this.tlacitko8 = (Button)findViewById(R.id.tlacitko8);
this.tlacitko9 = (Button)findViewById(R.id.tlacitko9);
this.rovnaSe = (Button)findViewById(R.id.tlacitkoRovnaSe);
this.plus = (Button)findViewById(R.id.tlacitkoPlus);
this.minus = (Button)findViewById(R.id.tlacitkoMinus);
tlacitko1.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
text_na_displeji[postup] = "1";
postup++;
for(int i=0; i < text_na_displeji.length; i++){
vysledek += text_na_displeji[i];
Display.setText(vysledek);
}
}
});
tlacitko2.setOnClickListener(new View.OnClickListener(){
@Override
public void onClick(View view){
text_na_displeji[postup] = "2";
postup++;
for(int i=0; i < text_na_displeji.length; i++){
vysledek += text_na_displeji[i];
Display.setText(vysledek);
}
}
});
tlacitko3.setOnClickListener(new View.OnClickListener(){
@Override
public void onClick(View view){
text_na_displeji[postup] = "3";
postup++;
for(int i=0; i < text_na_displeji.length; i++){
vysledek += text_na_displeji[i];
Display.setText(vysledek);
}
}
});
tlacitko4.setOnClickListener(new View.OnClickListener(){
@Override
public void onClick(View view){
text_na_displeji[postup] = "4";
postup++;
for(int i=0; i < text_na_displeji.length; i++){
vysledek += text_na_displeji[i];
Display.setText(vysledek);
}
}
});
tlacitko5.setOnClickListener(new View.OnClickListener(){
@Override
public void onClick(View view){
text_na_displeji[postup] = "5";
postup++;
for(int i=0; i < text_na_displeji.length; i++){
vysledek += text_na_displeji[i];
Display.setText(vysledek);
}
}
});
tlacitko6.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
text_na_displeji[postup] = "6";
postup++;
for(int i=0; i < text_na_displeji.length; i++){
vysledek += text_na_displeji[i];
Display.setText(vysledek);
}
}
});
tlacitko7.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
text_na_displeji[postup] = "7";
postup++;
for(int i=0; i < text_na_displeji.length; i++){
vysledek += text_na_displeji[i];
Display.setText(vysledek);
}
}
});
tlacitko8.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
text_na_displeji[postup] = "8";
postup++;
for(int i=0; i < text_na_displeji.length; i++){
vysledek += text_na_displeji[i];
Display.setText(vysledek);
}
}
});
tlacitko9.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
text_na_displeji[postup] = "9";
postup++;
for(int i=0; i < text_na_displeji.length; i++){
vysledek += text_na_displeji[i];
Display.setText(vysledek);
}
}
});
rovnaSe.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
boolean poprve = false;
boolean poprveZnak = false;
boolean plus = true;
int temp = 0;
int tempCislo1 = 0;
int tempCislo2 = 0;
for(int i =0; i < text_na_displeji.length; i++){
if(text_na_displeji[i] == "+" || text_na_displeji[i] == "-"){
if(poprveZnak == false){
for(int j = 0; j < i-1; j++){
tempCislo1 += array[j];
}
poprveZnak = true;
temp = i;
if(text_na_displeji[i] == "+"){
plus = true;
}
else plus = false;
}
else if(poprveZnak == true){
for(int j = temp; j < i-1; j++){
tempCislo2 += array[j];
}
temp = i;
if(plus == true){
konecnyVysledek += (tempCislo1+tempCislo2);
tempCislo1 = 0;
}
else{
konecnyVysledek += (tempCislo1-tempCislo2);
tempCislo1 =0;
}
if(text_na_displeji[i] == "+") plus=true;
else plus=false;
}
}
else array[i] = Integer.parseInt(text_na_displeji[i]);
}
String temp22 = "Vysledek je: " + konecnyVysledek;
Display.setText(temp22);
}
});
plus.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
text_na_displeji[postup] = "+";
postup++;
for(int i=0; i < text_na_displeji.length; i++){
vysledek += text_na_displeji[i];
Display.setText(vysledek);
}
}
});
minus.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
text_na_displeji[postup] = "-";
postup++;
for(int i=0; i < text_na_displeji.length; i++){
vysledek += text_na_displeji[i];
Display.setText(vysledek);
}
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.my, 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.
int id = item.getItemId();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
}
當我點擊，例如，數字一（tlacitko1（我的語言）），我的程序崩潰。
這是logcat的輸出：
07-18 22:33:26.416 28199-28199/com.bundas.tdsestr.kalkulacka D/dalvikvm﹕ Late-enabling CheckJNI
07-18 22:33:26.496 28199-28199/com.bundas.tdsestr.kalkulacka W/Trace﹕ error opening trace file: No such file or directory (2)
07-18 22:33:26.936 28199-28199/com.bundas.tdsestr.kalkulacka D/libEGL﹕ loaded /system/lib/egl/libEGL_tegra.so
07-18 22:33:26.956 28199-28199/com.bundas.tdsestr.kalkulacka D/libEGL﹕ loaded /system/lib/egl/libGLESv1_CM_tegra.so
07-18 22:33:26.956 28199-28199/com.bundas.tdsestr.kalkulacka D/libEGL﹕ loaded /system/lib/egl/libGLESv2_tegra.so
07-18 22:33:26.986 28199-28199/com.bundas.tdsestr.kalkulacka D/OpenGLRenderer﹕ Enabling debug mode 0
07-18 22:33:34.856 28199-28199/com.bundas.tdsestr.kalkulacka D/AndroidRuntime﹕ Shutting down VM
07-18 22:33:34.856 28199-28199/com.bundas.tdsestr.kalkulacka W/dalvikvm﹕ threadid=1: thread exiting with uncaught exception (group=0x40dd2930)
07-18 22:33:34.856 28199-28199/com.bundas.tdsestr.kalkulacka E/AndroidRuntime﹕ FATAL EXCEPTION: main
java.lang.NullPointerException
at com.bundas.tdsestr.kalkulacka.MyActivity$9.onClick(MyActivity.java:140)
at android.view.View.performClick(View.java:4211)
at android.view.View$PerformClick.run(View.java:17362)
at android.os.Handler.handleCallback(Handler.java:725)
at android.os.Handler.dispatchMessage(Handler.java:92)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:5227)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:795)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:562)
at de.robv.android.xposed.XposedBridge.main(XposedBridge.java:133)
at dalvik.system.NativeStart.main(Native Method)
我的XML代碼：
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin"
tools:context=".MyActivity">
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="1"
android:id="@+id/tlacitko1"
android:layout_marginLeft="162dp"
android:layout_centerVertical="true"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="2"
android:id="@+id/tlacitko2"
android:layout_marginLeft="37dp"
android:layout_alignTop="@+id/tlacitko1"
android:layout_toRightOf="@+id/tlacitko1" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="3"
android:id="@+id/tlacitko3"
android:layout_marginLeft="37dp"
android:layout_alignBottom="@+id/tlacitko2"
android:layout_toRightOf="@+id/tlacitko2" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="4"
android:id="@+id/tlacitko4"
android:layout_below="@+id/tlacitko1"
android:layout_alignLeft="@+id/tlacitko1"
android:layout_alignStart="@+id/tlacitko1"
android:layout_marginTop="38dp" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="5"
android:id="@+id/tlacitko5"
android:layout_alignTop="@+id/tlacitko4"
android:layout_alignLeft="@+id/tlacitko2"
android:layout_alignStart="@+id/tlacitko2" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="6"
android:id="@+id/tlacitko6"
android:layout_alignTop="@+id/tlacitko5"
android:layout_alignLeft="@+id/tlacitko3"
android:layout_alignStart="@+id/tlacitko3" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="7"
android:id="@+id/tlacitko7"
android:layout_below="@+id/tlacitko4"
android:layout_alignLeft="@+id/tlacitko4"
android:layout_alignStart="@+id/tlacitko4"
android:layout_marginTop="38dp" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="8"
android:id="@+id/tlacitko8"
android:layout_alignTop="@+id/tlacitko7"
android:layout_alignLeft="@+id/tlacitko5"
android:layout_alignStart="@+id/tlacitko5" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="9"
android:id="@+id/tlacitko9"
android:layout_alignTop="@+id/tlacitko8"
android:layout_alignLeft="@+id/tlacitko6"
android:layout_alignStart="@+id/tlacitko6" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="-"
android:id="@+id/tlacitkoMinus"
android:layout_below="@+id/tlacitko7"
android:layout_alignRight="@+id/tlacitko8"
android:layout_alignEnd="@+id/tlacitko8"
android:layout_marginTop="47dp" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="+"
android:id="@+id/tlacitkoPlus"
android:layout_alignTop="@+id/tlacitkoMinus"
android:layout_toLeftOf="@+id/tlacitko2" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="="
android:id="@+id/tlacitkoRovnaSe"
android:layout_alignTop="@+id/tlacitkoMinus"
android:layout_alignLeft="@+id/tlacitko9"
android:layout_alignStart="@+id/tlacitko9" />
<TextView
android:layout_width="fill_parent"
android:layout_height="50dp"
android:id="@+id/display"
android:layout_centerHorizontal="true"
android:layout_alignParentTop="true"
android:textSize="30dp" />
</RelativeLayout>
謝謝你這麼多的時間。我今年15歲，我是一個非常糟糕的程序員..我主要在Linux的C/C++中編程...
無論誰在壓低QS，試着去理解一個C/C++程序員的心態，在那裏定義一個結構變量會自動使它非空。對於那些從C/C++切換到Java的人來說，這是一個經常犯的錯誤。沒有理由downvote。 –