android - android中的阶乘程序

Question

嘿伙计们，我知道有很多 java 程序用于数字的阶乘...但是我遇到了 android 的问题。以下是我的代码....谢谢

package com.droidacid.apticalc.aptitudes;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

import com.droidacid.apticalc.R;

public class AptiFactorial extends Activity implements android.view.View.OnClickListener{
EditText number;
TextView answer;
Button calculate;

long factorial = 1;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.apti_factorial);
    initialize();
    calcFactorial();
}
private void initialize() {
    number = (EditText) findViewById(R.id.et_apti_number);
    answer = (TextView) findViewById(R.id.tv_apti_answer);
    calculate = (Button) findViewById(R.id.b_apti_calc);
    calculate.setOnClickListener(this);
}
private void calcFactorial() {
    if (number.getText().toString().equals("")) number.setText("0");
    int num = Integer.parseInt(number.getText().toString());
    for(int i = 1; i<=num; i++){
        factorial = i * factorial;
    }

}


@Override
public void onClick(View v) {
    calcFactorial();
    answer.setText("Factorial of " + number.getText().toString() + " is : " +     factorial);

}

}

这是我的代码，我需要知道一种设置提示而不是 0 的方法，但是如果我删除 if (number.getText().toString().equals("")) 数字。 setText("0");

然后得到 NullPointerException...同样在一开始它的计算正确但如果我再次计算然后得到错误的答案。我认为是一些循环问题，因为我直接使用阶乘的值。

请帮忙谢谢

Answer 1

忘掉所有equal 的东西，涵盖所有基础并像这样做:

package com.droidacid.apticalc.aptitudes;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

import com.droidacid.apticalc.R;

public class AptiFactorial extends Activity implements android.view.View.OnClickListener{
EditText number;
TextView answer;
Button calculate;

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

private void initialize() {
    number = (EditText) findViewById(R.id.et_apti_number);
    number.setHint("Enter number to be factorialized :P")
    answer = (TextView) findViewById(R.id.tv_apti_answer);
    calculate = (Button) findViewById(R.id.b_apti_calc);
    calculate.setOnClickListener(this);
}

private long calcFactorial() {

    long factorial = 1;
    try {
        factorial = Long.parseLong(number.getText().toString());
        for(int i=factorial-1; i>0; i--){
            factorial = i * factorial;
        }
    } catch (NumberFormatException e) {
        Toast.makeText(this, "Incorrect Input", Toast.LENGTH_LONG).show();
    } finally {}

    return factorial;
}

@Override
public void onClick(View v) {
    answer.setText("Factorial of " + number.getText().toString() + " is : " + calcFactorial());
}