test-paper-system/src/PrimaryMaker.java

package Program;

public class PrimaryMaker extends QuestionMaker {
    private static final char[] operators = {'+', '-', '*', '/'};

    /**
     * 添加括号
     * @param expression 原式
     * @return 添加括号后的式子
     */

    protected String BracketsMaker(String expression){
        String[] sum = expression.split(" ");

        // 只有当式子长度>=5时才添加括号
        if(sum.length >= 5){
            int maxStart = (sum.length - 5) / 2;
            if(maxStart > 0){
                int start = (rand.nextInt(maxStart) + 1) * 2;
                int minEnd = start + 2;
                int maxEnd = Math.min(sum.length - 3, start + 4);

                if(maxEnd > minEnd){
                    int end = minEnd + (rand.nextInt((maxEnd - minEnd) / 2 + 1)) * 2;
                    StringBuilder result = getBuilder(sum, start, end);
                    return result.toString();
                }
            }

            // 如果上述逻辑没有添加括号，强制在前三个元素周围添加括号
            StringBuilder result = new StringBuilder();
            result.append("(").append(sum[0]).append(" ").append(sum[1]).append(" ").append(sum[2]).append(")");
            for(int i = 3; i < sum.length; i++){
                result.append(" ").append(sum[i]);
            }
            return result.toString();
        }

        // 对于长度<5的短式，直接返回原式，不添加括号
        return expression;
    }

    private static StringBuilder getBuilder(String[] sum, int start, int end) {
        StringBuilder result = new StringBuilder();
        for(int i = 0; i < sum.length; i++){
            if(i == start){
                result.append("(");
            }
            result.append(sum[i]);
            if(i == end){
                result.append(")");
            }
            if(i < sum.length - 1){
                result.append(" ");
            }
        }
        return result;
    }

    @Override
    protected String makeOneQuestion() {
        int count = rand.nextInt(4) + 2;
        StringBuilder question = new StringBuilder();

        question.append(randomMaker());

        for(int i = 1; i < count; i++){
            char operator = operators[rand.nextInt(operators.length)];
            int randNum = randomMaker();
            question.append(" ").append(operator).append(" ").append(randNum);
        }
        return BracketsMaker(question.toString());
    }

    @Override
    protected boolean checkQuestion(String question) {
        return question.matches("[0-9+\\-*/() ]+");
    }
}