partner_project/src/generator/Problem.java

package generator;

import java.util.List;
import java.util.Collections;

public class Problem {
    private final String expression;
    private final double result;
    private final List<String> options;
    private final String correctAnswerOption;

    public Problem(String expression, double result, List<String> options,
                   String correctAnswerOption) {
        this.expression = expression;
        this.result = result;
        this.options = options;
        this.correctAnswerOption = correctAnswerOption;
    }

    public String getQuestionText() {
        return "计算: " + expression + " = ?";
    }

    public String getExpression() {
        return expression;
    }

    public List<String> getOptions() {
        return Collections.unmodifiableList(options);
    }

    public String getCorrectAnswerOption() {
        return formatResult(result);
    }
    
    private String formatResult(double result) {
        if (Double.isNaN(result)) {
            return "Error";
        }
        if (Math.abs(result - Math.round(result)) < 0.0001) {
            return String.valueOf((int) Math.round(result));
        }
        return String.format("%.2f", result);
    }

    public double getResult() {
        return result;
    }

    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder();
        sb.append(getQuestionText()).append("\n");
        char optionChar = 'A';
        for (String option : options) {
            sb.append(optionChar++).append(". ").append(option).append("  ");
        }
        sb.append("\n正确答案: ").append(correctAnswerOption);
        return sb.toString();
    }
}