如果不重写.equals()， ==和.equals()都指向同一个对象。

一旦你重写了.equals()，你想要做的就是你的愿望。你可以比较调用对象的状态和传入对象的状态或者你可以调用super。equals()

一般来说，你问题的答案是“是的”，但是……

.equals(...) will only compare what it is written to compare, no more, no less. If a class does not override the equals method, then it defaults to the equals(Object o) method of the closest parent class that has overridden this method. If no parent classes have provided an override, then it defaults to the method from the ultimate parent class, Object, and so you're left with the Object#equals(Object o) method. Per the Object API this is the same as ==; that is, it returns true if and only if both variables refer to the same object, if their references are one and the same. Thus you will be testing for object equality and not functional equality. Always remember to override hashCode if you override equals so as not to "break the contract". As per the API, the result returned from the hashCode() method for two objects must be the same if their equals methods show that they are equivalent. The converse is not necessarily true.

如果不重写.equals()， ==和.equals()都指向同一个对象。

一旦你重写了.equals()，你想要做的就是你的愿望。你可以比较调用对象的状态和传入对象的状态或者你可以调用super。equals()

例1 -

==和.equals方法只用于引用比较。它表示两个对象是否引用同一个对象。

对象类等于方法实现

public class HelloWorld{
     public static void main(String []args){
       Object ob1 = new Object();
       Object ob2 = ob1;
       System.out.println(ob1 == ob2); // true
       System.out.println(ob1.equals(ob2)); // true
     }    
}

例2 -

但是如果我们想要使用equals方法比较对象的内容，那么class必须重写对象的类equals()方法并提供内容比较的实现。这里，String类重写了用于内容比较的equals方法。所有包装器类都覆盖了用于内容比较的equals方法。

字符串类等于方法实现

public class HelloWorld{
     public static void main(String []args){
       String ob1 = new String("Hi");
       String ob2 = new String("Hi");
       System.out.println(ob1 == ob2); // false (Both references are referring two different objects)
       System.out.println(ob1.equals(ob2)); // true
     }
}

例3 -

对于String，还有一个用例。在这里，当我们将任何字符串赋值给string引用时，字符串常量就会在string常量池中创建。如果将相同的字符串赋值给新的字符串引用，则不会创建新的字符串常量，而是引用现有的字符串常量。

public class HelloWorld{
     public static void main(String []args){
       String ob1 = "Hi";
       String ob2 = "Hi";
       System.out.println(ob1 == ob2); // true
       System.out.println(ob1.equals(ob2)); // true
     }
}

注意，每当重写hashCode方法时，通常都需要重写该方法，以便维护hashCode方法的一般契约，该契约规定相等的对象必须具有相等的散列码。

Java API equals()方法契约

简单地说，==检查两个对象是否指向相同的内存位置，而.equals()计算对象中值的比较。

public class StringPool {

public static void main(String[] args) {

    String s1 = "Cat";// will create reference in string pool of heap memory
    String s2 = "Cat";
    String s3 = new String("Cat");//will create a object in heap memory

    // Using == will give us true because same reference in string pool

    if (s1 == s2) {
        System.out.println("true");
    } else {
        System.out.println("false");
    }

    // Using == with reference and Object will give us False

    if (s1 == s3) {
        System.out.println("true");
    } else {
        System.out.println("false");
    }

    // Using .equals method which refers to value

    if (s1.equals(s3)) {
        System.out.println("true");
    } else {
        System.out.println("False");
    }

    }
  }

——输出 真正的 假 真正的