Is following class immutable and how can it be changed into immutable class?

Is following class immutable and how can it be changed into immutable class? Is it true that if you remove last getLoanDate-method, then you have immutable class and why is that so?

public class Loan {
private double annualInterestRate;
private int numberOfYears;
private double loanAmount;
private java.util.Date loanDate;

/** Default constructor */
public Loan() {
this(2.5, 1, 1000);
}

/** Construct a loan with specified annual interest rate,
number of years and loan amount
*/
public Loan(double annualInterestRate, int numberOfYears,
double loanAmount) {
this.annualInterestRate = annualInterestRate;
this.numberOfYears = numberOfYears;
this.loanAmount = loanAmount;
loanDate = new java.util.Date();
}

/** Return annualInterestRate */
public double getAnnualInterestRate() {
return annualInterestRate;
}

/** Return numberOfYears */
public int getNumberOfYears() {
return numberOfYears;
}

/** Return loanAmount */
public double getLoanAmount() {
return loanAmount;
}

/** Find monthly payment */
public double getMonthlyPayment() {
double monthlyInterestRate = annualInterestRate / 1200;
double monthlyPayment = loanAmount * monthlyInterestRate / (1 -
(Math.pow(1 / (1 + monthlyInterestRate), numberOfYears * 12)));
return monthlyPayment;
}

/** kuukausimaksu K * q^n * ( (1-q)/(1-q^n)
missä q = 1 + vuosikorko/1200
*/
public double kuukausiEra() {
double q = 1 + annualInterestRate / 1200;
int n = numberOfYears * 12;
double qn = Math.pow(q, n);
double era = loanAmount * qn * ((1 - q) / (1 - qn));
return era;
}

/** Find total payment */
public double getTotalPayment() {
double totalPayment = getMonthlyPayment() * numberOfYears * 12;
return totalPayment;
}

/** Return loan date */
public java.util.Date getLoanDate() {
return loanDate;
}
}