JTextArea 输出乱码

[politeboy]

java eclipse gui 中 JTextArea 中输出 一个类中的tostring（重写函数，调用double 类型返回函数CalculateMPayment()）结果输出的不是数字，而是乱码NaN

public double calculateMPayment() {
		double j=0.0;
		if(jobStatus.equalsIgnoreCase("G")) {
			j=0.025/12;
		}
		else if(jobStatus.equalsIgnoreCase("P")) {
			j=0.0425/12;
		}
		return loanMount*j/(1-Math.pow(1+j, -durationYear*12));
	}


public String toString() {   
		return "Name:   "+name+"\nNRIC NUMBER:   "+icNum+"\nLoan Amount:   "+loanMount+"\nDuration:   "+
	            durationYear+"\nJob Status:   "+jobStatus+"\nMonthly Payment:   "+calculateMPayment();
	}