Question

是否有一种简单的方法可以将列表类型从String更改为Float并将其也应用于其他列表？无需使代码复杂。我曾经使用过Python，因此android和java语法使我搞砸了很多事情

我得到了一个csv文件，其中第一列包含字符串值，其余列包含浮点值。我想在调用list.get（value_id）

时从列表获取Float数据

以下代码：

package com.example.nick.calcy;

import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.List;

public class Mix extends AppCompatActivity {
InputStream inputStream;
List<String> komponenty,em,bi,ws,ca,fs,na,L,M = new ArrayList<>();
String[] ids;
EditText et1,et2,et3,et4,et5,et6,et7;
Float sum;
Button buttonSum;

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_mix);

    et1 = findViewById(R.id.editText11);

    et2 = findViewById(R.id.editText12);

    et3 = findViewById(R.id.editText13);

    et4 = findViewById(R.id.editText14);

    et5 = findViewById(R.id.editText15);

    et6 = findViewById(R.id.editText16);

    et7 = findViewById(R.id.editText17);

    buttonSum = findViewById(R.id.button11);


    /**Loading the input file*/
    inputStream = getResources().openRawResource(R.raw.brojler);

    BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream));
    try {
        String csvLine;
        while ((csvLine = reader.readLine()) != null) {

            ids=csvLine.split(",");
            try{
                komponenty.add(ids[0]);
                em.add(ids[1]);
                bi.add(ids[2]);
                ws.add(ids[3]);
                ca.add(ids[4]);
                fs.add(ids[5]);
                na.add(ids[6]);
                L.add(ids[7]);
                M.add(ids[8]);

            }catch (Exception e){
                Log.e("Unknown error",e.toString());
            }
        }

    }
    catch (IOException ex) {
        throw new RuntimeException("Error in reading CSV file: "+ex);
    }

    /** button activity*/
    buttonSum.setOnClickListener(new View.OnClickListener(){
        public void onClick(View v){
            if(et1.getText().toString().trim().length() == 0 || 
                    et2.getText().toString().trim().length() == 0 || 
                    et3.getText().toString().trim().length() == 0 || 
                    et4.getText().toString().trim().length() == 0 || 
                    et5.getText().toString().trim().length() == 0 || 
                    et6.getText().toString().trim().length() == 0 || 
                    et7.getText().toString().trim().length() == 0) {
                CharSequence text = "Blank fields detected";
                Toast.makeText(getApplicationContext(), text, Toast.LENGTH_LONG).show();
            }
            else{
            Intent i = new Intent(getApplicationContext(),Summary.class);
            Float x1 = Float.parseFloat(et1.getText().toString());
            Float x2 = Float.parseFloat(et2.getText().toString());
            Float x3 = Float.parseFloat(et3.getText().toString());
            Float x4 = Float.parseFloat(et4.getText().toString());
            Float x5 = Float.parseFloat(et5.getText().toString());
            Float x6 = Float.parseFloat(et6.getText().toString());
            Float x7 = Float.parseFloat(et7.getText().toString());

            sum = x1+x2+x3+x4+x5+x6+x7;

            i.putExtra("x1", x1);
            i.putExtra("x2", x2);
            i.putExtra("x3", x3);
            i.putExtra("x4", x4);
            i.putExtra("x5", x5);
            i.putExtra("x6", x6);
            i.putExtra("x7", x7);

            if (sum == 100){
                startActivity(i);
            } else{
                CharSequence text = "Sum must equal 100%";
                Toast.makeText(getApplicationContext(), text, Toast.LENGTH_LONG).show();
            }
        }}
    });
}
}

我有2个主意

更改我读取csv文件的方式我试图那样做

Float ids2;
ids2 = Float.parseFloat(csvLine.split(","));

然后将其添加到准备好的列表中，但是我弄乱了数据类型

第二个想法写函数，将简单地根据其ID从列表中转换单个值的数据类型

private Float getFloat(List list, int id)
{
 Object value;
 String step2;
 Float changed;
 value = list.get(id);
 step2 = value.toString();
 changed = Float.parseFloat(step2);
 return changed;
}

可悲的是，它在使用时崩溃了我的应用程序

09-03 17:42:39.166 18888-18888/com.example.nick.calcy E/MessageQueue-JNI: java.lang.NullPointerException: Attempt to invoke interface method 'java.lang.Object java.util.List.get(int)' on a null object reference

@编辑其实我发现了一个问题，我没有正确填写列表，试图解决该问题

@编辑2 调试器显示，我无法从原始文件夹中获取数据。

E/Unknown error: java.lang.NullPointerException: Attempt to invoke interface method 'boolean java.util.List.add(java.lang.Object)' on a null object reference
E/Unknown error: java.lang.NullPointerException: Attempt to invoke interface method 'boolean java.util.List.add(java.lang.Object)' on a null object reference
E/Unknown error: java.lang.NullPointerException: Attempt to invoke interface method 'boolean java.util.List.add(java.lang.Object)' on a null object reference
I/chatty: uid=10083(u0_a83) com.example.nick.calcy expire 8 lines
E/Unknown error: java.lang.NullPointerException: Attempt to invoke interface method 'boolean java.util.List.add(java.lang.Object)' on a null object reference

立即使用该代码

package com.example.nick.calcy;

import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.List;

public class Mix extends AppCompatActivity {
    InputStream inputStream;
    List<String> komponenty = new ArrayList<String>();
    List<String> em = new ArrayList<String>();
    String[] ids;
    EditText et1,et2,et3,et4,et5,et6,et7;
    Float sum,x11;
    Button buttonSum;
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_mix);
    et1 = findViewById(R.id.editText11);
    et2 = findViewById(R.id.editText12);
    et3 = findViewById(R.id.editText13);
    et4 = findViewById(R.id.editText14);
    et5 = findViewById(R.id.editText15);
    et6 = findViewById(R.id.editText16);
    et7 = findViewById(R.id.editText17);
    buttonSum = findViewById(R.id.button11);
    inputStream = getResources().openRawResource(R.raw.brojler);
    BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream));
    try {
        String csvLine;
        while ((csvLine = reader.readLine()) != null)
        {
            ids=csvLine.split(",");
            try{
                komponenty.add(ids[0]);
                em.add(ids[1]);

            }
            catch (Exception e){
                Log.e("Unknown error",e.toString());
            }
        }

    }
    catch (IOException ex) {
        throw new RuntimeException("Error in reading CSV file: "+ex);
    }

    /** button activity*/
    buttonSum.setOnClickListener(new View.OnClickListener(){
        public void onClick(View v){
            if(et1.getText().toString().trim().length() == 0 ||
                    et2.getText().toString().trim().length() == 0 ||
                    et3.getText().toString().trim().length() == 0 ||
                    et4.getText().toString().trim().length() == 0 ||
                    et5.getText().toString().trim().length() == 0 ||
                    et6.getText().toString().trim().length() == 0 ||
                    et7.getText().toString().trim().length() == 0) {
                CharSequence text = "Blank fields detected";
                Toast.makeText(getApplicationContext(), text, Toast.LENGTH_LONG).show();
            }
            else{
            Intent i = new Intent(getApplicationContext(),Summary.class);
            Float x1 = Float.parseFloat(et1.getText().toString());
            Float x2 = Float.parseFloat(et2.getText().toString());
            Float x3 = Float.parseFloat(et3.getText().toString());
            Float x4 = Float.parseFloat(et4.getText().toString());
            Float x5 = Float.parseFloat(et5.getText().toString());
            Float x6 = Float.parseFloat(et6.getText().toString());
            Float x7 = Float.parseFloat(et7.getText().toString());

            sum = x1+x2+x3+x4+x5+x6+x7;
            x11 = 100*getFloat(em,0);

            i.putExtra("x1", x1);
            i.putExtra("x2", x2);
            i.putExtra("x3", x3);
            i.putExtra("x4", x4);
            i.putExtra("x5", x5);
            i.putExtra("x6", x6);
            i.putExtra("x7", x7);

            if (sum == 100){
                startActivity(i);
            } else{
                CharSequence text1 = "Sum must equal 100%";
                Toast.makeText(getApplicationContext(), text1, Toast.LENGTH_LONG).show();
            }
        }}
    });
}
private Float getFloat(List<String> list, int id)
{
 String value = list.get(id);
 return Float.parseFloat(value);
}
}

Answer 1

通常有更优雅的解决方案，但是作为快速解决方案，您可以将功能更改为：

private Float getSum(List<String> list)
{
    Float sum = 0f;
    if (!list.isEmpty() && list.size() > 1) {
        for (int i = 1; i < list.size(); i++) {
            sum+= Float.parseFloat(list.get(i));
        }
    }
    return sum;
}

Answer 2

尝试一下：遍历List<String>并将每个项目转换为Float，然后将其添加到List<Float>。

我写了这个函数，它使用List<String>并返回一个List<Float>。我希望它对您有用。

List<Float> getList(List<String> stringList)
{
    List<Float> floatList = new ArrayList<>();

    for (int i = 0; i < stringList.size(); i++)
    {
        Float number = Float.valueOf(stringList.get(i));
        floatList.add(number);
    }

    return floatList;
}

然后，像这样调用函数：

List<Float> floats = getList(strings);

Answer 3

这就是您所需要的：

   private List<Float> getList(List<String> stringList)
    {
        List<Float> floatList = new ArrayList<>();

        for (int i = 0; i < stringList.size(); i++)
        {
            Float number = Float.valueOf(stringList.get(i));
            floatList.add(number);
        }

        return floatList;
    }

如何将List <string>转换为List <float> Android

3 个答案: