如果重写equals（）方法，是否可以在Java中比较对类实例的引用？

Question

I need to compare 2 instances of a class, that has equals method overridden - it returns string that equal concatenation of parameters. But I need be sure that exists only 1 instance. For this I think to check references.

Is it possible in java?

Answer 1

Use == to compare the references. It's enough to make sure if different variables refer to the same instance.

Answer 2

The easy way to ensure that only one instance exists is to use an Enum.

public enum MyEnum {

    NameOfSingleton("aPropertyValue");

    private String aProperty;

    private MyEnum(String aProperty) {
        this.aProperty = aProperty
    }

    public getAProperty() {
        return this.aProperty;


}

Using it is just as simple.

MyEnum.NameOfSingleton.getAProperty();

This doesn't really address your equality question, but it addresses your need for a singleton instance of a class.

Answer 3

I'm not entirely sure what you're trying to do, but if you need to ensure that only one instance of something exists then you can use the static keyword to do so. There are multiple ways you could ensure this with static, for instance creating a static variable called count that keeps track of how many instances of the object have been made. Then in the constructor for the object you just increment count. To see if there is more than one instance of the object you just check the count variable and it should tell you.