Question

我正在编写一个使用array.length的程序。我想知道找到array.length的下划线代码是多么昂贵。我想知道继续使用array.length或创建一个int aLength = array.length并在整个程序中使用它会更好。我在网上看到一篇文章，说当使用for循环时，应该使用array.length，当不在for循环中时，aLength变量更好。再一次，在具有多个for循环的程序中使用array.length是否更好？或者设置变量并使用它更好吗？与整个string.substring（0,10）或者字符串tempString = string.subtstring（0,10）一样和tempString一样吗？

import java.io.BufferedReader;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.io.InputStream;
import java.net.URL;
import java.util.ResourceBundle;
import java.util.logging.Level;
import java.util.logging.Logger;
import javafx.application.Platform;
import javafx.event.ActionEvent;
import javafx.fxml.FXML;
import javafx.fxml.Initializable;
import javafx.scene.control.Label;


public class FXMLDocumentController implements Initializable {

@FXML private Label lblLeader;

File batchMarc = null;
BufferedReader bufferedreader = null;
InputStream inputstream = null;
String preProcessedRecords = null;
String[] processedRecords = null;
int counter = 0, prLength = 0;



@Override
public void initialize(URL url, ResourceBundle rb) {
    try 
    {
        batchMarc = new File("batchMarc.mrc");
        bufferedreader = new BufferedReader(new FileReader(batchMarc));
        String line;

        while((line = bufferedreader.readLine()) != null)
        {                 
            preProcessedRecords = line;                
        }

        processedRecords = extractIndividualRecords(preProcessedRecords);
        prLength = processedRecords.length;//sets prLength to the length of he processedRecords array

        for(int i = 0; i < prLength; i++)
        {
            System.out.println(processedRecords[i]);
        }

        bufferedreader.close();
    } 
    catch (FileNotFoundException ex) 
    {
  Logger.getLogger(FXMLDocumentController.class.getName()).log(Level.SEVERE, null, ex);
    } catch (IOException ex) 
    {
        Logger.getLogger(FXMLDocumentController.class.getName()).log(Level.SEVERE, null, ex);
    }
}    

private String[] extractIndividualRecords(String preProcessed)
{

    String [] processed = preProcessed.split("\\x1D");       

    return processed;
}

@FXML
private void handleButtonActionNext(ActionEvent event) {

    if(counter < prLength && counter > -1)
    {
        String tempLeader = processedRecords[counter].substring(0, 24);
        Platform.runLater(() -> lblLeader.setText(tempLeader));
        counter++;
         System.out.println(counter);                    
    }          
    else if(counter == -1)
    {
        counter = 1;
        String tempLeader = processedRecords[counter].substring(0, 24);
        Platform.runLater(() -> lblLeader.setText(tempLeader));
        counter++;
        System.out.println(counter);   
    }
}

@FXML
private void handleButtonActionPrevious(ActionEvent event) {
    if(counter >= 0 && counter < prLength)
    {
        String tempLeader = processedRecords[counter].substring(0, 24);
        Platform.runLater(() -> lblLeader.setText(tempLeader));
        counter--;
        System.out.println(counter);                             
    }   
    else if(counter == prLength)
    {
        counter = prLength - 2;
        String tempLeader = processedRecords[counter].substring(0, 24);
        Platform.runLater(() -> lblLeader.setText(tempLeader));
        counter--;
        System.out.println(counter);   
    }
}
}

Answer 1

使用引用var总是更好，而不是函数调用，有一个计算涉及获取arr.length / subString（），并且必须对循环的每次迭代重复此计算。而对于参考var，此计算仅执行一次。

在具有多个for循环的程序中使用array.length是否更好？或者设置变量并使用它更好吗？

1 个答案: