Java字符串比较不起作用？

Question

我想它很简单,但我无法理解如何做到这一点:(我已经尝试了==和等于目前为止,但我没有让它们工作.这是一个小编程计算瑞典语的成绩highschool系统(所以只需忽略瑞典语并查看字符串比较.这里的问题是统计函数变量在程序结束时仍然设置为0.

import javax.swing.*;

public class Uppgift1 {
private String[] subjects = {"Matematik","Svenska","Engelska","Idrott",
            "Bild","Fysik","Biologi","Kemi","Historia","Geografi",
            "Samhällskunskap","Religionskunskap"};`

private String[] grades = new String[subjects.length]; // Lika många element som ämnen

public void setGrades() {
    for(int i = 0; i < grades.length; i++){
        grades[i] = JOptionPane.showInputDialog("Ange betyg i " + subjects[i] + " (IG, G, VG, MVG)");
    }
}

public void statistics() {
    int ig = 0;
    int g = 0;
    int vg = 0;
    int mvg = 0;
    int points = 0;

    for(int i = 0; i < grades.length; i++){
        if(grades[i].equals("IG")){
            ig++;
        }

        else if(grades[i] == "G"){
            g++;
            points += 10;
        }

        else if(grades[i] == "VG"){
            vg++;
            points += 15;
        }

        else if(grades[i] == "MVG"){
            mvg++;
            points += 20;
        }
    }

    String output = new String("BETYGSSTATISTIK\n");
    output += "IG: " + ig + "\n";
    output += "G: " + g + "\n";
    output += "VG: " + vg + "\n";
    output += "MVG: " + mvg + "\n";
    output += "Betygspoäng: " + points;

    JOptionPane.showMessageDialog(null, output);
}

public static void main(String[] args) {
    Uppgift1 prog = new Uppgift1();
    prog.setGrades();
    prog.statistics();
}
}

Answer 1

你已经正确使用了第一个比较,但是后来,你得到了错误的方法.

equals()在比较字符串的内容时总是使用方法,就像在第一种情况下那样.

此外,如果它不能以某种方式工作,可能是因为你的字符串中有空格leading或trailing空格.尝试这样使用它: -

if (grades[i].trim().equals("IG"))