java - 在 Java 中覆盖 equals()

Question

我试图了解“equals()”在 Java 中的工作原理。特别是与“toString()”相比。这是一个让我偏离正轨的例子。

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public class Car
{
    String make, model;

    public Car( String model, String make )
    {
        this.make  = model;
        this.model = make;
    }   

    public String toString()
    {
        String str = "This is a car. ";
        str += "Make: " + make + " | Model: " + model;
        return str;
    }

    public boolean equals( Car c )
    {
        return ( make.equals( c.make ) && model.equals( c.model ) );
    }
}

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public class Node 
{
    protected Object obj;
    protected Node next;

    public Node( Object o )
    {
        this.obj = o;
        this.next = null;
    }

    public String toString()
    {
        return obj.toString();
    }

    public boolean equals( Node n )
    {
        return ( this.obj.equals( n.obj ) );
    }
}

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Car c1 = new Car("toyota", "corolla");
Car c2 = new Car("toyota", "corolla");

Node nC1 = new Node( c1 );
Node nC2 = new Node( c2 );

nC1.print();
nC2.print();


if( nC1.equals( nC2 ) )
    System.out.println("They are equal!");
else
    System.out.println("They are NOT equal!");

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此处 nC1.print() 和 nC2.print() 的行为符合预期。打印:

This is a car. Make: toyota | Model: corolla
This is a car. Make: toyota | Model: corolla

然而nC1.equals( nC2 ), 打印:

"They are NOT equal!"

简而言之，问题是我可以覆盖“toString()”，但不能覆盖“equals()”。我错过了什么？我想对此行为有一个简单的解释。

Answer 1

我认为您应该将方法的签名保留为:

public boolean equals(Object obj)

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作为旁注:将 @Override 注释放在您要覆盖的方法中，以确保您覆盖的是正确的方法，否则编译器会报错。