java.lang.NullPointerException：尝试在空对象引用上调用虚方法'boolean java.util.Vector.add（java.lang.Object）'

Question

我正在尝试制作课程安排应用。但是，我遇到了一个问题，我不知道如何解决它。

我环顾四周，Google和StackOverflow尽可能找到了一些信息。但是，我没有得到它的工作。现在希望我可以获得有关代码的帮助。

我在Android开发方面相对缺乏经验。我的代码很难看。如果你能提高我的代码质量，我将非常感激你。

提前致谢。

MainActivity.java

package com.example.lee.myapplication;

import android.content.ContentValues;
import android.content.Intent;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

import java.util.Vector;

import butterknife.Bind;
import butterknife.ButterKnife;
import butterknife.OnClick;

public class MainActivity extends AppCompatActivity {

    private MyDatabaseHelper dbHelper;
    private Vector<Course_lee> courseList;
    private TextView tv_mainActivity;


    @Bind(R.id.back)
    Button back;
    @Bind(R.id.week)
    TextView week;
    @Bind(R.id.set)
    Button set;
    @Bind(R.id.mon)
    TextView mon;
    @Bind(R.id.tue)
    TextView tue;
    @Bind(R.id.wed)
    TextView wed;
    @Bind(R.id.thur)
    TextView thur;
    @Bind(R.id.fri)
    TextView fri;
    @Bind(R.id.sta)
    TextView sta;
    @Bind(R.id.sun)
    TextView sun;
    @Bind(R.id.textView1_1)
    TextView textView11;
    @Bind(R.id.textView1_2)
    TextView textView12;
    @Bind(R.id.textView1_3)
    TextView textView13;
    @Bind(R.id.textView1_4)
    TextView textView14;
    @Bind(R.id.textView1_5)
    TextView textView15;
    @Bind(R.id.textView1_6)
    TextView textView16;
    @Bind(R.id.textView1_7)
    TextView textView17;
    @Bind(R.id.textView2_1)
    TextView textView21;
    @Bind(R.id.textView2_2)
    TextView textView22;
    @Bind(R.id.textView2_3)
    TextView textView23;
    @Bind(R.id.textView2_4)
    TextView textView24;
    @Bind(R.id.textView2_5)
    TextView textView25;
    @Bind(R.id.textView2_6)
    TextView textView26;
    @Bind(R.id.textView2_7)
    TextView textView27;
    @Bind(R.id.textView3_1)
    TextView textView31;
    @Bind(R.id.textView3_2)
    TextView textView32;
    @Bind(R.id.textView3_3)
    TextView textView33;
    @Bind(R.id.textView3_4)
    TextView textView34;
    @Bind(R.id.textView3_5)
    TextView textView35;
    @Bind(R.id.textView3_6)
    TextView textView36;
    @Bind(R.id.textView3_7)
    TextView textView37;
    @Bind(R.id.textView4_1)
    TextView textView41;
    @Bind(R.id.textView4_2)
    TextView textView42;
    @Bind(R.id.textView4_3)
    TextView textView43;
    @Bind(R.id.textView4_4)
    TextView textView44;
    @Bind(R.id.textView4_5)
    TextView textView45;
    @Bind(R.id.textView4_6)
    TextView textView46;
    @Bind(R.id.textView4_7)
    TextView textView47;
    @Bind(R.id.textView5_1)
    TextView textView51;
    @Bind(R.id.textView5_2)
    TextView textView52;
    @Bind(R.id.textView5_3)
    TextView textView53;
    @Bind(R.id.textView5_4)
    TextView textView54;
    @Bind(R.id.textView5_5)
    TextView textView55;
    @Bind(R.id.textView5_6)
    TextView textView56;
    @Bind(R.id.textView5_7)
    TextView textView57;
    @Bind(R.id.textView6_1)
    TextView textView61;
    @Bind(R.id.textView6_2)
    TextView textView62;
    @Bind(R.id.textView6_3)
    TextView textView63;
    @Bind(R.id.textView6_4)
    TextView textView64;
    @Bind(R.id.textView6_5)
    TextView textView65;
    @Bind(R.id.textView6_6)
    TextView textView66;
    @Bind(R.id.textView6_7)
    TextView textView67;
    @Bind(R.id.textView7_1)
    TextView textView71;
    @Bind(R.id.textView7_2)
    TextView textView72;
    @Bind(R.id.textView7_3)
    TextView textView73;
    @Bind(R.id.textView7_4)
    TextView textView74;
    @Bind(R.id.textView7_5)
    TextView textView75;
    @Bind(R.id.textView7_6)
    TextView textView76;
    @Bind(R.id.textView7_7)
    TextView textView77;
    @Bind(R.id.textView8_1)
    TextView textView81;
    @Bind(R.id.textView8_2)
    TextView textView82;
    @Bind(R.id.textView8_3)
    TextView textView83;
    @Bind(R.id.textView8_4)
    TextView textView84;
    @Bind(R.id.textView8_5)
    TextView textView85;
    @Bind(R.id.textView8_6)
    TextView textView86;
    @Bind(R.id.textView8_7)
    TextView textView87;

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

        ButterKnife.bind(this);

        dbHelper = new MyDatabaseHelper(this, "CourseStore.db", null, 1);
        SQLiteDatabase db =dbHelper.getWritableDatabase();
        Cursor cursor = db.rawQuery("select * from course", null);
        first_init(db,cursor);
        init(cursor);
        cursor.close();
    }

    private void first_init(SQLiteDatabase db,Cursor cursor) {
        if (!cursor.moveToFirst()) {

            Log.e("tag", String.valueOf(new Course_lee(R.id.textView1_1).getId()));
            courseList.add(new Course_lee(R.id.textView1_1));
            courseList.add(new Course_lee(R.id.textView1_2));
            courseList.add(new Course_lee(R.id.textView1_3));
            courseList.add(new Course_lee(R.id.textView1_4));
            courseList.add(new Course_lee(R.id.textView1_5));
            courseList.add(new Course_lee(R.id.textView1_6));
            courseList.add(new Course_lee(R.id.textView1_7));
            courseList.add(new Course_lee(R.id.textView2_1));
            courseList.add(new Course_lee(R.id.textView2_2));
            courseList.add(new Course_lee(R.id.textView2_3));
            courseList.add(new Course_lee(R.id.textView2_4));
            courseList.add(new Course_lee(R.id.textView2_5));
            courseList.add(new Course_lee(R.id.textView2_6));
            courseList.add(new Course_lee(R.id.textView2_7));
            courseList.add(new Course_lee(R.id.textView3_1));
            courseList.add(new Course_lee(R.id.textView3_2));
            courseList.add(new Course_lee(R.id.textView3_3));
            courseList.add(new Course_lee(R.id.textView3_4));
            courseList.add(new Course_lee(R.id.textView3_5));
            courseList.add(new Course_lee(R.id.textView3_6));
            courseList.add(new Course_lee(R.id.textView3_7));
            courseList.add(new Course_lee(R.id.textView4_1));
            courseList.add(new Course_lee(R.id.textView4_2));
            courseList.add(new Course_lee(R.id.textView4_3));
            courseList.add(new Course_lee(R.id.textView4_4));
            courseList.add(new Course_lee(R.id.textView4_5));
            courseList.add(new Course_lee(R.id.textView4_6));
            courseList.add(new Course_lee(R.id.textView4_7));
            courseList.add(new Course_lee(R.id.textView5_1));
            courseList.add(new Course_lee(R.id.textView5_2));
            courseList.add(new Course_lee(R.id.textView5_3));
            courseList.add(new Course_lee(R.id.textView5_4));
            courseList.add(new Course_lee(R.id.textView5_5));
            courseList.add(new Course_lee(R.id.textView5_6));
            courseList.add(new Course_lee(R.id.textView5_7));
            courseList.add(new Course_lee(R.id.textView6_1));
            courseList.add(new Course_lee(R.id.textView6_2));
            courseList.add(new Course_lee(R.id.textView6_3));
            courseList.add(new Course_lee(R.id.textView6_4));
            courseList.add(new Course_lee(R.id.textView6_5));
            courseList.add(new Course_lee(R.id.textView6_6));
            courseList.add(new Course_lee(R.id.textView6_7));
            courseList.add(new Course_lee(R.id.textView7_1));
            courseList.add(new Course_lee(R.id.textView7_2));
            courseList.add(new Course_lee(R.id.textView7_3));
            courseList.add(new Course_lee(R.id.textView7_4));
            courseList.add(new Course_lee(R.id.textView7_5));
            courseList.add(new Course_lee(R.id.textView7_6));
            courseList.add(new Course_lee(R.id.textView7_7));
            courseList.add(new Course_lee(R.id.textView8_1));
            courseList.add(new Course_lee(R.id.textView8_2));
            courseList.add(new Course_lee(R.id.textView8_3));
            courseList.add(new Course_lee(R.id.textView8_4));
            courseList.add(new Course_lee(R.id.textView8_5));
            courseList.add(new Course_lee(R.id.textView8_6));
            courseList.add(new Course_lee(R.id.textView8_7));


            insertPrimaryTable(courseList,db);
        }

    }

    private void insertPrimaryTable(Vector<Course_lee> courseList,SQLiteDatabase db) {
        int id;
        for (int i=0;i<courseList.size();i++){

            id=courseList.elementAt(i).getId();
            ContentValues values = new ContentValues();
            values.put("id", id);
            db.insert("course", null, values);
            values.clear();
        }
    }


    private void setWeek() {

    }

    private void init(Cursor cursor) {

        //Cursor cursor = db.rawQuery("select * from course where day=? and time=?", new String[] {"1",""});
        //Cursor cursor = db.rawQuery("select * from course",null);

        if (cursor.moveToFirst()) {
            do {

                int id=cursor.getInt(cursor.getColumnIndex("id"));
                String name = cursor.getString(cursor.getColumnIndex("name"));
                String num = cursor.getString(cursor.getColumnIndex("num"));
                String teacher = cursor.getString(cursor.getColumnIndex("teacher"));
                int jieshu =cursor.getInt(cursor.getColumnIndex("jieshu"));
                int weekBegin =cursor.getInt(cursor.getColumnIndex("weekBegin"));
                int weekEnd =cursor.getInt(cursor.getColumnIndex("weekEnd"));
                int flag=cursor.getInt(cursor.getColumnIndex("flag"));
                String time=cursor.getString(cursor.getColumnIndex("time"));
                int day = cursor.getInt(cursor.getColumnIndex("day"));


                tv_mainActivity= (TextView) findViewById(id);
                tv_mainActivity.setText(name);

                if (!courseList.isEmpty()){
                    for (int i=0;i<courseList.size();i++){

                        if(courseList.elementAt(i).getId()==id){
                            courseList.elementAt(i).setName(name);
                            courseList.elementAt(i).setClassNum(num);
                            courseList.elementAt(i).setTeacher(teacher);
                            courseList.elementAt(i).setJieshu(jieshu);
                            courseList.elementAt(i).setWeekBegin(weekBegin);
                            courseList.elementAt(i).setWeekEnd(weekEnd);
                            courseList.elementAt(i).setFlag(flag);
                            courseList.elementAt(i).setTime(time);
                            courseList.elementAt(i).setDay(day);
                            break;
                        }
                    }
                }
            } while (cursor.moveToNext());
        }



    }


    void highlight(){

    }

    void updateTable(String name,String num){


    }

    private void enterDetail(Course_lee course) {
        Intent intent = new Intent(MainActivity.this, DetailActivity.class);
        intent.putExtra("course", course);
        startActivity(intent);
    }


    @OnClick({R.id.back, R.id.set, R.id.textView1_1, R.id.textView1_2, R.id.textView1_3, R.id.textView1_4, R.id.textView1_5, R.id.textView1_6, R.id.textView1_7, R.id.textView2_1, R.id.textView2_2, R.id.textView2_3, R.id.textView2_4, R.id.textView2_5, R.id.textView2_6, R.id.textView2_7, R.id.textView3_1, R.id.textView3_2, R.id.textView3_3, R.id.textView3_4, R.id.textView3_5, R.id.textView3_6, R.id.textView3_7, R.id.textView4_1, R.id.textView4_2, R.id.textView4_3, R.id.textView4_4, R.id.textView4_5, R.id.textView4_6, R.id.textView4_7, R.id.textView5_1, R.id.textView5_2, R.id.textView5_3, R.id.textView5_4, R.id.textView5_5, R.id.textView5_6, R.id.textView5_7, R.id.textView6_1, R.id.textView6_2, R.id.textView6_3, R.id.textView6_4, R.id.textView6_5, R.id.textView6_6, R.id.textView6_7, R.id.textView7_1, R.id.textView7_2, R.id.textView7_3, R.id.textView7_4, R.id.textView7_5, R.id.textView7_6, R.id.textView7_7, R.id.textView8_1, R.id.textView8_2, R.id.textView8_3, R.id.textView8_4, R.id.textView8_5, R.id.textView8_6, R.id.textView8_7})
    public void onClick(View view) {
        Course_lee course;
        switch (view.getId()) {
            case R.id.back:
                finish();
                break;
            case R.id.set:

                break;
            case R.id.textView1_1:
                course=findCorrectCourse(R.id.textView1_1);
                enterDetail(course);
                break;
            case R.id.textView1_2:
                course=findCorrectCourse(R.id.textView1_2);
                enterDetail(course);
                break;
            case R.id.textView1_3:
                course=findCorrectCourse(R.id.textView1_3);
                enterDetail(course);
                break;
            case R.id.textView1_4:
                course=findCorrectCourse(R.id.textView1_4);
                enterDetail(course);
                break;
            case R.id.textView1_5:
                break;
            case R.id.textView1_6:
                break;
            case R.id.textView1_7:
                break;
            case R.id.textView2_1:
                break;
            case R.id.textView2_2:
                break;
            case R.id.textView2_3:
                break;
            case R.id.textView2_4:
                break;
            case R.id.textView2_5:
                break;
            case R.id.textView2_6:
                break;
            case R.id.textView2_7:
                break;
            case R.id.textView3_1:
                break;
            case R.id.textView3_2:
                break;
            case R.id.textView3_3:
                break;
            case R.id.textView3_4:
                break;
            case R.id.textView3_5:
                break;
            case R.id.textView3_6:
                break;
            case R.id.textView3_7:
                break;
            case R.id.textView4_1:
                break;
            case R.id.textView4_2:
                break;
            case R.id.textView4_3:
                break;
            case R.id.textView4_4:
                break;
            case R.id.textView4_5:
                break;
            case R.id.textView4_6:
                break;
            case R.id.textView4_7:
                break;
            case R.id.textView5_1:
                break;
            case R.id.textView5_2:
                break;
            case R.id.textView5_3:
                break;
            case R.id.textView5_4:
                break;
            case R.id.textView5_5:
                break;
            case R.id.textView5_6:
                break;
            case R.id.textView5_7:
                break;
            case R.id.textView6_1:
                break;
            case R.id.textView6_2:
                break;
            case R.id.textView6_3:
                break;
            case R.id.textView6_4:
                break;
            case R.id.textView6_5:
                break;
            case R.id.textView6_6:
                break;
            case R.id.textView6_7:
                break;
            case R.id.textView7_1:
                break;
            case R.id.textView7_2:
                break;
            case R.id.textView7_3:
                break;
            case R.id.textView7_4:
                break;
            case R.id.textView7_5:
                break;
            case R.id.textView7_6:
                break;
            case R.id.textView7_7:
                break;
            case R.id.textView8_1:
                break;
            case R.id.textView8_2:
                break;
            case R.id.textView8_3:
                break;
            case R.id.textView8_4:
                break;
            case R.id.textView8_5:
                break;
            case R.id.textView8_6:
                break;
            case R.id.textView8_7:
                break;
        }
    }

    private Course_lee findCorrectCourse(int tv) {
        Course_lee course;
        for (int i=0;i<courseList.size();i++) {
            if (courseList.elementAt(i).getId() == tv) {
                course=courseList.elementAt(i);
                return course;
            }
        }
        return null;
    }

}

Course_lee.java

package com.example.lee.myapplication;

import android.os.Parcel;
import android.os.Parcelable;

public class Course_lee implements Parcelable {

    private int id;
    private String name;
    private String classNum;
    private String teacher;
    private int jieshu;
    private int weekBegin;
    private int weekEnd;
    private int flag;
    private String time;
    private int day;

    public Course_lee(int id, String name, String classNum, String teacher, int jieshu, int weekBegin, int weekEnd, int flag, String time, int day) {
        this.id = id;
        this.name = name;
        this.classNum = classNum;
        this.teacher = teacher;
        this.jieshu = jieshu;
        this.weekBegin = weekBegin;
        this.weekEnd = weekEnd;
        this.flag = flag;
        this.time = time;
        this.day = day;
    }

    public Course_lee(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getClassNum() {
        return classNum;
    }

    public void setClassNum(String classNum) {
        this.classNum = classNum;
    }

    public String getTeacher() {
        return teacher;
    }

    public void setTeacher(String teacher) {
        this.teacher = teacher;
    }

    public int getJieshu() {
        return jieshu;
    }

    public void setJieshu(int jieshu) {
        this.jieshu = jieshu;
    }

    public int getWeekBegin() {
        return weekBegin;
    }

    public void setWeekBegin(int weekBegin) {
        this.weekBegin = weekBegin;
    }

    public int getWeekEnd() {
        return weekEnd;
    }

    public void setWeekEnd(int weekEnd) {
        this.weekEnd = weekEnd;
    }

    public int getFlag() {
        return flag;
    }

    public void setFlag(int flag) {
        this.flag = flag;
    }

    public String getTime() {
        return time;
    }

    public void setTime(String time) {
        this.time = time;
    }

    public int getDay() {
        return day;
    }

    public void setDay(int day) {
        this.day = day;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    @Override
    public int describeContents() {
        return 0;
    }

    @Override
    public void writeToParcel(Parcel dest, int flags) {
        dest.writeInt(this.id);
        dest.writeString(this.name);
        dest.writeString(this.classNum);
        dest.writeString(this.teacher);
        dest.writeInt(this.jieshu);
        dest.writeInt(this.weekBegin);
        dest.writeInt(this.weekEnd);
        dest.writeInt(this.flag);
        dest.writeString(this.time);
        dest.writeInt(this.day);
    }

    protected Course_lee(Parcel in) {
        this.id = in.readInt();
        this.name = in.readString();
        this.classNum = in.readString();
        this.teacher = in.readString();
        this.jieshu = in.readInt();
        this.weekBegin = in.readInt();
        this.weekEnd = in.readInt();
        this.flag = in.readInt();
        this.time = in.readString();
        this.day = in.readInt();
    }

    public static final Creator<Course_lee> CREATOR = new Creator<Course_lee>() {
        @Override
        public Course_lee createFromParcel(Parcel source) {
            return new Course_lee(source);
        }

        @Override
        public Course_lee[] newArray(int size) {
            return new Course_lee[size];
        }
    };
}

MyDatabaseHelper.java

package com.example.lee.myapplication;

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.widget.Toast;

public class MyDatabaseHelper extends SQLiteOpenHelper {


    public static final String CREATE_COURSE="create table course("
            +"id integer primary key, "
            + "name text, "
            + "num text, "
            + "teacher text, "
            + "jieshu integer,"
            + "weekBegin integer,"
            + "weekEnd integer,"
            + "flag integer,"
            + "time text,"
            + "day integer)";



    public MyDatabaseHelper(Context context, String name, SQLiteDatabase.CursorFactory factory, int version) {
        super(context, name, factory, version);

    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL(CREATE_COURSE);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

    }
}

logcat的

03-25 11:36:34.647 10013-10013/com.example.lee.myapplication E/AndroidRuntime: FATAL EXCEPTION: main
                                                                           Process: com.example.lee.myapplication, PID: 10013
                                                                           java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.lee.myapplication/com.example.lee.myapplication.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.util.Vector.add(java.lang.Object)' on a null object reference
                                                                               at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)
                                                                               at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
                                                                               at android.app.ActivityThread.-wrap11(ActivityThread.java)
                                                                               at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
                                                                               at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                               at android.os.Looper.loop(Looper.java:148)
                                                                               at android.app.ActivityThread.main(ActivityThread.java:5417)
                                                                               at java.lang.reflect.Method.invoke(Native Method)
                                                                               at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
                                                                               at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
                                                                            Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.util.Vector.add(java.lang.Object)' on a null object reference
                                                                               at com.example.lee.myapplication.MainActivity.first_init(MainActivity.java:181)
                                                                               at com.example.lee.myapplication.MainActivity.onCreate(MainActivity.java:171)
                                                                               at android.app.Activity.performCreate(Activity.java:6237)
                                                                               at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107)
                                                                               at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369)
                                                                               at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476) 
                                                                               at android.app.ActivityThread.-wrap11(ActivityThread.java) 
                                                                               at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344) 
                                                                               at android.os.Handler.dispatchMessage(Handler.java:102) 
                                                                               at android.os.Looper.loop(Looper.java:148) 
                                                                               at android.app.ActivityThread.main(ActivityThread.java:5417) 
                                                                               at java.lang.reflect.Method.invoke(Native Method) 
                                                                               at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 
                                                                               at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) 

Answer 1

您没有初始化courselist。在数据库交互之前将其添加到onCreate

private Vector<Course_lee> courseList = new Vector<Course_lee>();