java - 空指针异常是什么原因

Question

大家好，我尝试做计算器，我编写了以下代码，当我尝试运行它时，出现空指针异常，我不知道错误是什么，我发现我的代码很好，没有错误 该函数在布局出现之前强制关闭并且 onclickerlistener 中的所有内容因此至少当我单击任何按钮时我必须强制关闭如果有问题请帮助我这是我的代码:

    package com.example.calculato;

    import android.os.Bundle;
    import android.app.Activity;
    import android.util.Log;
    import android.view.Menu;
    import android.view.View;
    import android.view.View.OnClickListener;
    import android.widget.Button;
    import android.widget.EditText;

    public class MainActivity extends Activity implements OnClickListener{

         EditText edt;

            double  num1=0,num2=0,result=0;
            double fact=1;

            String a="";
            char  op;
            boolean b=false;
            Button b1,b2,b3,b4,b5,b6,b7,b8,b9,b10,b11,b12,b13,b14,b15,b16,b17,b18,b19,b20,b21;  

        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
            Log.d("inside on create ", "okzzzzzzzzzzzzzzzzz");
            edt=(EditText)findViewById(R.id.editText1);
             b1=(Button)findViewById(R.id.button1);
             b2=(Button)findViewById(R.id.button2);
             b3=(Button)findViewById(R.id.button3);
             b4=(Button)findViewById(R.id.button4);
             b5=(Button)findViewById(R.id.button5);
             b6=(Button)findViewById(R.id.button6);
             b7=(Button)findViewById(R.id.button7);
             b8=(Button)findViewById(R.id.button8);
             b9=(Button)findViewById(R.id.button9);
             b10=(Button)findViewById(R.id.button10);
             b11=(Button)findViewById(R.id.button11);
             b12=(Button)findViewById(R.id.button12);
             b13=(Button)findViewById(R.id.button13);
             b14=(Button)findViewById(R.id.button14);
             b15=(Button)findViewById(R.id.button15);
             b16=(Button)findViewById(R.id.button16);
             Log.d("after def  ", "okzzzzzzzzzzzzzzzzz");
             b1.setOnClickListener(new View.OnClickListener() {

                    @Override
                    public void onClick(View v) {
                        // TODO Auto-generated method stub
                        a=edt.getText().toString();
                          edt.setText(a+ "1");

                    }
                });

              b2.setOnClickListener(new View.OnClickListener() {

                    @Override
                    public void onClick(View v) {
                        // TODO Auto-generated method stub
                        a=edt.getText().toString();
                          edt.setText(a+ "2");

                    }
                });

              b3.setOnClickListener(new View.OnClickListener() {

                    @Override
                    public void onClick(View v) {
                        // TODO Auto-generated method stub
                        a=edt.getText().toString();
                          edt.setText(a+ "3");

                    }
                });

              b4.setOnClickListener(new View.OnClickListener() {

                    @Override
                    public void onClick(View v) {
                        // TODO Auto-generated method stub
                        a=edt.getText().toString();
                          edt.setText(a+ "4");  
                    }
                });
              b5.setOnClickListener(new View.OnClickListener() {

                    @Override
                    public void onClick(View v) {
                        // TODO Auto-generated method stub
                        a=edt.getText().toString();
                          edt.setText(a+ "5");

                    }
                });
              b6.setOnClickListener(new View.OnClickListener() {

                    @Override
                    public void onClick(View v) {
                        // TODO Auto-generated method stub
                        a=edt.getText().toString();
                          edt.setText(a+ "6");

                    }
                });

              b7.setOnClickListener(new View.OnClickListener() {

                    @Override
                    public void onClick(View v) {
                        // TODO Auto-generated method stub
                        a=edt.getText().toString();
                          edt.setText(a+ "7");

                    }
                });

              b8.setOnClickListener(new View.OnClickListener() {

                    @Override
                    public void onClick(View v) {
                        // TODO Auto-generated method stub
                        a=edt.getText().toString();
                          edt.setText(a+ "8");


                    }
                });
              b9.setOnClickListener(new View.OnClickListener() {

                    @Override
                    public void onClick(View v) {
                        // TODO Auto-generated method stub
                        a=edt.getText().toString();
                          edt.setText(a+ "9");

                    }
                });
              b10.setOnClickListener(new View.OnClickListener() {

                    @Override
                    public void onClick(View v) {
                        // TODO Auto-generated method stub
                        a=edt.getText().toString();
                          edt.setText(a+ "0");  
                    }
                });

              b13.setOnClickListener(new View.OnClickListener() {

                    @Override
                    public void onClick(View v) {
                        // TODO Auto-generated method stub
                        num1=Double.valueOf(edt.getText().toString());
                        op='+';
                        edt.setText("");




                    }
                });
              b14.setOnClickListener(new View.OnClickListener() {

                    @Override
                    public void onClick(View v) {
                        // TODO Auto-generated method stub
                         num1=Double.valueOf(edt.getText().toString());
                        op='-';
                        edt.setText("");


                    }
                });
              b15.setOnClickListener(new View.OnClickListener() {

                    @Override
                    public void onClick(View v) {
                        // TODO Auto-generated method stub
                         num1=Double.valueOf(edt.getText().toString());
                        op='*';
                        edt.setText("");


                    }
                });
              b16.setOnClickListener(new View.OnClickListener() {

                    @Override
                    public void onClick(View v) {
                        // TODO Auto-generated method stub
                         num1=Double.valueOf(edt.getText().toString());
                        op='/';
                        edt.setText("");


                    }
                });
              b11.setOnClickListener(new View.OnClickListener() {

                    @Override
                    public void onClick(View v) {
                        // TODO Auto-generated method stub

                        edt.setText(" ");




                    }
                });



                 b12.setOnClickListener(new OnClickListener() {

                    @Override
                    public void onClick(View arg0) {
                        // TODO Auto-generated method stub

                        try {
                            String Value = edt.getText().toString();
                            if(Value.length()==1)
                                edt.setText("");
                            else 
                            {
                            Value = Value.substring(0,Value.length()-1);
                            edt.setText(Value);
                            }
                        } catch (Exception e) {

                        }

                    }
                });
                 b17.setOnClickListener(new View.OnClickListener() {

                        @Override
                        public void onClick(View v) {
                            // TODO Auto-generated method stub
                             num2=Double.valueOf(edt.getText().toString());

                            if(op=='+')
                            {
                                result=num1+num2;
                                 edt.setText(String.valueOf(result));

                            }
                            if(op=='-')
                            {
                                result=num1-num2;
                                 edt.setText(String.valueOf(result));

                            }
                            if(op=='*')
                            {
                                result=num1*num2;
                                 edt.setText(String.valueOf(result));

                            }
                            if(op=='/')
                                {

                                if(num2!=0)
                                {
                                    result=num1/num2;
                                     edt.setText(String.valueOf(result));
                                    }
                                else
                                    edt.setText("Math Error");
                                }

                        }
                    });

        }

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

        @Override
        public void onClick(View v) {
            // TODO Auto-generated method stub

        }

    }

这是 logcat :

            10-28 14:16:22.488: E/AndroidRuntime(1049): FATAL EXCEPTION: main
    10-28 14:16:22.488: E/AndroidRuntime(1049): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.calculato/com.example.calculato.MainActivity}: java.lang.NullPointerException
    10-28 14:16:22.488: E/AndroidRuntime(1049):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
    10-28 14:16:22.488: E/AndroidRuntime(1049):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
    10-28 14:16:22.488: E/AndroidRuntime(1049):     at android.app.ActivityThread.access$600(ActivityThread.java:141)
    10-28 14:16:22.488: E/AndroidRuntime(1049):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
    10-28 14:16:22.488: E/AndroidRuntime(1049):     at android.os.Handler.dispatchMessage(Handler.java:99)
    10-28 14:16:22.488: E/AndroidRuntime(1049):     at android.os.Looper.loop(Looper.java:137)
    10-28 14:16:22.488: E/AndroidRuntime(1049):     at android.app.ActivityThread.main(ActivityThread.java:5039)
    10-28 14:16:22.488: E/AndroidRuntime(1049):     at java.lang.reflect.Method.invokeNative(Native Method)
    10-28 14:16:22.488: E/AndroidRuntime(1049):     at java.lang.reflect.Method.invoke(Method.java:511)
    10-28 14:16:22.488: E/AndroidRuntime(1049):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
    10-28 14:16:22.488: E/AndroidRuntime(1049):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
    10-28 14:16:22.488: E/AndroidRuntime(1049):     at dalvik.system.NativeStart.main(Native Method)
    10-28 14:16:22.488: E/AndroidRuntime(1049): Caused by: java.lang.NullPointerException
    10-28 14:16:22.488: E/AndroidRuntime(1049):     at com.example.calculato.MainActivity.onCreate(MainActivity.java:254)
    10-28 14:16:22.488: E/AndroidRuntime(1049):     at android.app.Activity.performCreate(Activity.java:5104)
    10-28 14:16:22.488: E/AndroidRuntime(1049):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
    10-28 14:16:22.488: E/AndroidRuntime(1049):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)

Answer 1

希望这可以帮助您:b17 未初始化