Basic question, this is my first time using Comparable and compareTo... Why does not work?

[André Asantos]

Basic question, this is my first time using Comparable and compareTo... Why does not work? Runtime Expection... NullPointerException...

package corejava.comparetocomparablecompator2;

public class ContaCorrente implements Comparable<ContaPoupanca> {

	private int saldo;// = (int) 600.00;// casting

	public int getSaldo() {
		return saldo;
	}

	public void setSaldo(int saldo) {
		this.saldo = saldo;
	}

	public int compareTo(ContaPoupanca contaPoupanca) {
		if (getSaldo() == contaPoupanca.getSaldo()) {
			System.out.println("Saldo de CC é igual CP");
			return -1;
		}
		if (getSaldo() != contaPoupanca.getSaldo()) {
			System.out.println("Saldo de CC diferente de CP");
			return 0;
		}
		return 0;
	}
	
	public static void main(String[] args) {
		ContaPoupanca cp1 = new ContaPoupanca();
		cp1.setSaldo(100);
		
		new ContaCorrente().setSaldo(50);
		
		new ContaCorrente().compareTo(null);
	}
}

[Tom Reilly]

Because in the compareTo(ContaPoupanca contaPoupanca) method you are using contaPoupanca without checking to see that it is not null. In main(), you have new ContaCorrente().compareTo(null);

Also I noticed that in compareTo(ContaPoupanca contaPoupanca), you are returning -1 or 0. The compareTo() method should return three values; a negative number, 0, and a positive number.

[Tom Reilly]

Also, when implementing Comparable, you should compare two instances of the same class.

public class ContaCorrente implements Comparable<ContaPoupanca>

should be:

public class ContaCorrente implements Comparable<ContaCorrente>

[André Asantos]

if is possible, you could type the code for me I would love that... because I try to learn it by myself and that's really difficult... hehehe you all have been teaching me a lot...
bye,