求助：定义类的时候要不要给private变量赋初值？
各位高手，大家好，我是java初学者，现在有一个关于定义类时要不要给private型变量赋初值的问题。
有一个类，叫做Tax, 以下是它的完整定义：
class Tax {
public final static int SINGLE_FILER = 1;
public final static int MARRIED_JOINTLY = 2;
public final static int MARRIED_SEPARATELY = 3;
public final static int HEAD_OF_HOUSEHOLD = 4;
private int filingStatus = SINGLE_FILER;
private int[][] brackets = {
{27050, 65550, 136750, 297350}, // Single filer
{45200, 109250, 166500, 297350}, // married filing jointly
{22600, 54625, 83250, 148675}, // married filing separately
{36250, 93650, 151650, 297350} // head of household
};
private double[] rates = {0.15, 0.275, 0.305, 0.355, 0.391};
private double taxableIncome = 100000;
public Tax() {
}
public Tax(int filingStatus, int[][] brackets, double[] rates,
double taxableIncome) {
this.filingStatus = filingStatus;
this.brackets = brackets;
this.rates = rates;
this.taxableIncome = taxableIncome;
}
public void setBrackets(int[][] brackets) {
this.brackets = brackets;
}
public void setRates(double[] rates) {
this.rates = rates;
}
public double getTaxableIncome() {
return taxableIncome;
}
public void setTaxableIncome(double taxableIncome) {
this.taxableIncome = taxableIncome;
}
public int getFilingStatus() {
return filingStatus;
}
public void setFilingStatus(int filingStatus) {
this.filingStatus = filingStatus;
}
public double findTax() {
double tax = 0;
// Compute tax in the first bracket
if (taxableIncome <= brackets[filingStatus][0])
return tax = taxableIncome * rates[0];
else
tax = brackets[filingStatus][0] * rates[0];
int i;
// Compute tax in the possible 2nd, 3rd, 4th, and 5th brackets
for (i = 1; i < brackets[0].length; i++) {
if (taxableIncome > brackets[filingStatus][i])
tax += (brackets[filingStatus][i] - brackets[filingStatus][i - 1]) *
rates[i];
else {
tax += (taxableIncome - brackets[filingStatus][i - 1]) * rates[i];
break;
}
}
// Compute tax in the possible last bracket
if (i == brackets[0].length && taxableIncome > brackets[filingStatus][i - 1])
tax += (taxableIncome - brackets[filingStatus][i - 1]) * rates[i];
return tax;
}
}
这是题目给出的正确答案，它在定义这个类的时候给private型变量赋初值了，我现在有两个问题：
1. 我在测试这个类的时候，没给变量赋初值，而是直接在主程序里定义了两个Tax类的对象，然后用有参构造方法创建两个对象，同时赋给初值，程序运行得到了正确结果。那到底要不要在定义类的时候赋值呢？
2. 是不是任何一个类都应该有两个构造方法，有参和无参，如果在定义类的时候不赋初值，那是不是就必须要用有参构造方法给变量赋初值了呢？
谢谢大家的帮助！ |