java - 空指针异常 : null error

Question

这个问题已经有答案了:

What is a NullPointerException, and how do I fix it? (12 个回答)

已关闭 7 年前。

我有这个哈希集代码，当我尝试在其上运行我的编译方法时，我收到 Null Pointer Exception: null 错误。这是代码:

private void initKeywords() {
        keywords = new HashSet<String>();
        keywords.add("final");
        keywords.add("int");
        keywords.add("while");
        keywords.add("if");
        keywords.add("else");
        keywords.add("print");     
    }

    private boolean isIdent(String t) {
        if (keywords.contains(t)) {  ***//This is the line I get the Error***
            return false;
        }
        else if (t != null && t.length() > 0 && Character.isLetter(t.charAt(0))) {
            return true;
        }
        else {
            return false;
        }
    }

与此错误相关的其他行是:

public void compileProgram() {        
        System.out.println("compiling " + filename);
        while (theToken != null) {
            if (equals(theToken, "int") || equals(theToken, "final")) {
                compileDeclaration(true);
            } else {
                compileFunction(); //This line is giving an error with the above error
            }
        }
        cs.emit(Machine.HALT);
        isCompiled = true;
    }



private void compileFunction() {
        String fname = theToken;
        int entryPoint = cs.getPos();  
        if (equals(fname, "main")) {
            cs.setEntry(entryPoint);
        } 
        if (isIdent(theToken)) theToken = t.token(); ***//This line is giving an error***
        else t.error("expecting identifier, got " + theToken);

        symTable.allocProc(fname,entryPoint);


       accept("(");
        compileParamList();
        accept(")");
        compileCompound(true);
        if (equals(fname, "main")) cs.emit(Machine.HALT);
        else cs.emit(Machine.RET);
    }

Answer 1

您确定在 isIdent() 之前运行 initKeywords() 吗？