由于Java不支持操作符重载，==的行为是相同的 除equals()外的每个对象都可以使用is方法，该方法可以在 可以根据业务更改用于比较对象的Java和逻辑 规则。

在Java中==和=的主要区别是“==”被用来 建议检查equals()方法时比较原语 对象相等。

字符串比较是同时使用==和equals()方法的常见场景。由于java.lang.String类重写等于方法，它 如果两个String对象包含相同的内容，但== will返回true 只有当两个引用指向同一个对象时才返回true。

下面是一个使用==和equals()方法比较Java中两个string是否相等的例子，这将消除一些疑问:

 public class TEstT{

        public static void main(String[] args) {
            
    String text1 = new String("apple");
    String text2 = new String("apple");
          
    //since two strings are different object result should be false
    boolean result = text1 == text2;
    System.out.println("Comparing two strings with == operator: " + result);
          
    //since strings contains same content , equals() should return true
    result = text1.equals(text2);
    System.out.println("Comparing two Strings with same content using equals method: " + result);
          
    text2 = text1;
    //since both text2 and text1d reference variable are pointing to same object
    //"==" should return true
    result = (text1 == text2);
    System.out.println("Comparing two reference pointing to same String with == operator: " + result);

    }
    }

下面是关系运算符==和方法.equals()之间区别的一般规则。

object1 == object2比较object1和object2引用的对象是否指向Heap中的相同内存位置。

object1.equals(object2)比较object1和object2的值，而不管它们位于内存中的哪个位置。

可以使用String很好地演示这一点

场景1

 public class Conditionals {

    public static void main(String[] args) {
       String str1 = "Hello";
       String str2 = new String("Hello");
       System.out.println("is str1 == str2 ? " + (str1 == str2 ));
       System.out.println("is str1.equals(str2) ? " + (str1.equals(str2 )));
    }

 }



The result is
      is str1 == str2 ? false
      is str1.equals(str2) ? true 

场景2

public class Conditionals {

    public static void main(String[] args) {
       String str1 = "Hello";
       String str2 = "Hello";
       System.out.println("is str1 == str2 ? " + (str1 == str2 ));
       System.out.println("is str1.equals(str2) ? " + (str1.equals(str2 )));
    }

}

The result is 
  is str1 == str2 ? true
  is str1.equals(str2) ? true

这种字符串比较可以用作比较其他类型对象的基础。

例如，如果我有一个Person类，我需要定义比较两个Person的标准。假设person类有身高和体重的实例变量。

因此，创建person对象person1和person2，并使用.equals()来比较这两个对象，我需要重写person类的equals方法，以定义基于哪个实例变量(高度或重量)的比较。

但是，==操作符仍然会根据两个对象(person1和person2)的内存位置返回结果。

为了便于泛化这个人对象比较，我创建了以下测试类。对这些概念进行实验会发现大量的事实。

package com.tadtab.CS5044;

public class Person {

private double height;
private double weight;

public double getHeight() {
    return height;
}

public void setHeight(double height) {
    this.height = height;
}

public double getWeight() {
    return weight;
}

public void setWeight(double weight) {
    this.weight = weight;
}


@Override
public int hashCode() {
    final int prime = 31;
    int result = 1;
    long temp;
    temp = Double.doubleToLongBits(height);
    result = prime * result + (int) (temp ^ (temp >>> 32));
    return result;
}

@Override
/**
 * This method uses the height as a means of comparing person objects.
 * NOTE: weight is not part of the comparison criteria
 */
public boolean equals(Object obj) {
    if (this == obj)
        return true;
    if (obj == null)
        return false;
    if (getClass() != obj.getClass())
        return false;
    Person other = (Person) obj;
    if (Double.doubleToLongBits(height) != Double.doubleToLongBits(other.height))
        return false;
    return true;
}

public static void main(String[] args) {
    
    Person person1 = new Person();
    person1.setHeight(5.50);
    person1.setWeight(140.00);
    
    Person person2 = new Person();
    person2.setHeight(5.70);
    person2.setWeight(160.00);
    
    Person person3 = new Person();
    person3 = person2;
    
    Person person4 = new Person();
    person4.setHeight(5.70);
    
    Person person5 = new Person();
    person5.setWeight(160.00);
    
    System.out.println("is person1 == person2 ? " + (person1 == person2)); // false;
    System.out.println("is person2 == person3 ? " + (person2 == person3)); // true 
    //this is because perosn3 and person to refer to the one person object in memory. They are aliases;
    System.out.println("is person2.equals(person3) ? " + (person2.equals(person3))); // true;
    
    System.out.println("is person2.equals(person4) ? " + (person2.equals(person4))); // true;
    
    // even if the person2 and person5 have the same weight, they are not equal.
    // it is because their height is different
    System.out.println("is person2.equals(person4) ? " + (person2.equals(person5))); // false;
}

}

这个类执行的结果是:

is person1 == person2 ? false
is person2 == person3 ? true
is person2.equals(person3) ? true
is person2.equals(person4) ? true
is person2.equals(person4) ? false

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.

基本上，==比较两个对象在堆上是否有相同的引用，因此，除非两个引用链接到同一个对象，否则这种比较将为假。

equals()是继承自Object类的方法。默认情况下，如果两个对象具有相同的引用，则此方法进行比较。它的意思是:

object1.equals(object2) <=> object1 == object2

但是，如果您希望在同一类的两个对象之间建立相等性，则应该重写此方法。如果已经重写了equals()，重写hashCode()方法也是非常重要的。

当建立平等是Java对象契约的一部分时，实现hashCode()。如果你正在使用集合，并且你还没有实现hashCode()，可能会发生奇怪的糟糕事情:

HashMap<Cat, String> cats = new HashMap<>();
Cat cat = new Cat("molly");
cats.put(cat, "This is a cool cat");
System.out.println(cats.get(new Cat("molly"));

如果您没有实现hashCode()，则在执行前面的代码后将打印null。

对于String类:

equals()方法比较String实例中的“值”(在堆上)，而不考虑两个对象引用是否引用同一个String实例。如果任意两个String类型的对象引用引用同一个String实例，那就太好了!如果两个对象引用引用两个不同的String实例..这没什么区别。它是每个被比较的String实例中的“值”(即:字符数组的内容)。

On the other hand, the "==" operator compares the value of two object references to see whether they refer to the same String instance. If the value of both object references "refer to" the same String instance then the result of the boolean expression would be "true"..duh. If, on the other hand, the value of both object references "refer to" different String instances (even though both String instances have identical "values", that is, the contents of the character arrays of each String instance are the same) the result of the boolean expression would be "false".

就像任何解释一样，让它深入人心。

我希望这能让你清楚一点。

要在自定义类中使用equals函数，您必须重写equals函数(以及其他函数)。

equals方法比较对象。

==二进制操作符比较内存地址。