public: int CompareTo(System::Object ^ obj); public int CompareTo (object obj); public int CompareTo (object? obj); abstract member CompareTo : obj -> int Public Function CompareTo (obj As Object) As Integer Int32
A value that indicates the relative order of the objects being compared. The return value has these meanings:
| Less than zero | This instance precedes obj in the sort order. |
| Zero | This instance occurs in the same position in the sort order as obj. |
| Greater than zero | This instance follows obj in the sort order. |
Examples
The following example illustrates the use of CompareTo to compare a Temperature object implementing IComparable with another object. The Temperature object implements CompareTo by simply wrapping a call to the Int32.CompareTo method.
using namespace System; using namespace System::Collections; public ref class Temperature: public IComparable { /// <summary> /// IComparable.CompareTo implementation. /// </summary> protected: // The value holder Double m_value; public: virtual Int32 CompareTo( Object^ obj ) { if (obj == nullptr) return 1; if ( obj->GetType() == Temperature::typeid ) { Temperature^ temp = dynamic_cast<Temperature^>(obj); return m_value.CompareTo( temp->m_value ); } throw gcnew ArgumentException( "object is not a Temperature" ); } property Double Value { Double get() { return m_value; } void set( Double value ) { m_value = value; } } property Double Celsius { Double get() { return (m_value - 32) / 1.8; } void set( Double value ) { m_value = (value * 1.8) + 32; } } }; int main() { ArrayList^ temperatures = gcnew ArrayList; // Initialize random number generator. Random^ rnd = gcnew Random; // Generate 10 temperatures between 0 and 100 randomly. for (int ctr = 1; ctr <= 10; ctr++) { int degrees = rnd->Next(0, 100); Temperature^ temp = gcnew Temperature; temp->Value = degrees; temperatures->Add(temp); } // Sort ArrayList. temperatures->Sort(); for each (Temperature^ temp in temperatures) Console::WriteLine(temp->Value); return 0; } // The example displays the following output to the console (individual // values may vary because they are randomly generated): // 2 // 7 // 16 // 17 // 31 // 37 // 58 // 66 // 72 // 95 using System; using System.Collections; public class Temperature : IComparable { // The temperature value protected double temperatureF; public int CompareTo(object obj) { if (obj == null) return 1; Temperature otherTemperature = obj as Temperature; if (otherTemperature != null) return this.temperatureF.CompareTo(otherTemperature.temperatureF); else throw new ArgumentException("Object is not a Temperature"); } public double Fahrenheit { get { return this.temperatureF; } set { this.temperatureF = value; } } public double Celsius { get { return (this.temperatureF - 32) * (5.0/9); } set { this.temperatureF = (value * 9.0/5) + 32; } } } public class CompareTemperatures { public static void Main() { ArrayList temperatures = new ArrayList(); // Initialize random number generator. Random rnd = new Random(); // Generate 10 temperatures between 0 and 100 randomly. for (int ctr = 1; ctr <= 10; ctr++) { int degrees = rnd.Next(0, 100); Temperature temp = new Temperature(); temp.Fahrenheit = degrees; temperatures.Add(temp); } // Sort ArrayList. temperatures.Sort(); foreach (Temperature temp in temperatures) Console.WriteLine(temp.Fahrenheit); } } // The example displays the following output to the console (individual // values may vary because they are randomly generated): // 2 // 7 // 16 // 17 // 31 // 37 // 58 // 66 // 72 // 95 open System open System.Collections type Temperature() = // The temperature value let mutable temperatureF = 0. interface IComparable with member _.CompareTo(obj) = match obj with | null -> 1 | :? Temperature as other -> temperatureF.CompareTo other.Fahrenheit | _ -> invalidArg (nameof obj) "Object is not a Temperature" member _.Fahrenheit with get () = temperatureF and set (value) = temperatureF <- value member _.Celsius with get () = (temperatureF - 32.) * (5. / 9.) and set (value) = temperatureF <- (value * 9. / 5.) + 32. let temperatures = ResizeArray() // Initialize random number generator. let rnd = Random() // Generate 10 temperatures between 0 and 100 randomly. for _ = 1 to 10 do let degrees = rnd.Next(0, 100) let temp = Temperature(Fahrenheit=degrees) temperatures.Add temp // Sort ResizeArray. temperatures.Sort() for temp in temperatures do printfn $"{temp.Fahrenheit}" // The example displays the following output to the console (individual // values may vary because they are randomly generated): // 2 // 7 // 16 // 17 // 31 // 37 // 58 // 66 // 72 // 95 Imports System.Collections Public Class Temperature Implements IComparable ' The temperature value Protected temperatureF As Double Public Overloads Function CompareTo(ByVal obj As Object) As Integer _ Implements IComparable.CompareTo If obj Is Nothing Then Return 1 Dim otherTemperature As Temperature = TryCast(obj, Temperature) If otherTemperature IsNot Nothing Then Return Me.temperatureF.CompareTo(otherTemperature.temperatureF) Else Throw New ArgumentException("Object is not a Temperature") End If End Function Public Property Fahrenheit() As Double Get Return temperatureF End Get Set(ByVal Value As Double) Me.temperatureF = Value End Set End Property Public Property Celsius() As Double Get Return (temperatureF - 32) * (5/9) End Get Set(ByVal Value As Double) Me.temperatureF = (Value * 9/5) + 32 End Set End Property End Class Public Module CompareTemperatures Public Sub Main() Dim temperatures As New ArrayList ' Initialize random number generator. Dim rnd As New Random() ' Generate 10 temperatures between 0 and 100 randomly. For ctr As Integer = 1 To 10 Dim degrees As Integer = rnd.Next(0, 100) Dim temp As New Temperature temp.Fahrenheit = degrees temperatures.Add(temp) Next ' Sort ArrayList. temperatures.Sort() For Each temp As Temperature In temperatures Console.WriteLine(temp.Fahrenheit) Next End Sub End Module ' The example displays the following output to the console (individual ' values may vary because they are randomly generated): ' 2 ' 7 ' 16 ' 17 ' 31 ' 37 ' 58 ' 66 ' 72 ' 95Remarks
The CompareTo method is implemented by types whose values can be ordered or sorted. It is called automatically by methods of non-generic collection objects, such as Array.Sort, to order each member of the array. If a custom class or structure does not implement IComparable, its members cannot be ordered and the sort operation can throw an InvalidOperationException.
This method is only a definition and must be implemented by a specific class or value type to have effect. The meaning of the comparisons specified in the Return Value section ("precedes", "occurs in the same position as", and "follows") depends on the particular implementation.
By definition, any object compares greater than (or follows) null, and two null references compare equal to each other.
The parameter, obj, must be the same type as the class or value type that implements this interface; otherwise, an ArgumentException is thrown.
Notes to Implementers
For objects A, B and C, the following must be true:
A.CompareTo(A) must return zero.
If A.CompareTo(B) returns zero, then B.CompareTo(A) must return zero.
If A.CompareTo(B) returns zero and B.CompareTo(C) returns zero, then A.CompareTo(C) must return zero.
If A.CompareTo(B) returns a value other than zero, then B.CompareTo(A) must return a value of the opposite sign.
If A.CompareTo(B) returns a value x not equal to zero, and B.CompareTo(C) returns a value y of the same sign as x, then A.CompareTo(C) must return a value of the same sign as x and y.
Notes to Callers
Use the CompareTo(Object) method to determine the ordering of instances of a class.
Applies to
O método compareTo da classe String é utilizado para ordenar as Strings alfabeticamente*, e não por tamanho. Desta forma temos que "araraaaaaa" vem antes de "asa", e portanto o compareTo dá -1, porque ao comparar a primeira letra as duas Strings são iguais (a) e ao comparar a segunda, o r vem antes do s.
Para comparar as Strings por tamanho, você deveria invocar o método length das Strings e então comparar os tamanhos diretamente. (Sugestão do Marcelo Bonifazio)
Vale lembrar também que sempre que temos a.compareTo(b) retornando -1 (ou algum outro número negativo) significa que a antecede b, se retorna +1 (ou algum outro número positivo) então a sucede b e se retorna 0 então a e b são similares. Entrentanto a definição exata de "antecede", "sucede" e "similar" fica a critério de cada classe que implementa o compareTo. No caso da classe String a definição é dada pela ordenação alfabética*.
(*) - Na verdade a comparação não é exatamente alfabética, e sim é baseada em comparação de sequências de valores numéricos de codepoints unicode.