==What is the difference between and equals?

==： Operator , Used to compare base type variables with reference type variables .

For base type variables , Whether the compared variables hold the same values , The type does not have to be the same .

short s1 = 1; long l1 = 1;
//  result ：true. Different types , But the value is the same 
System.out.println(s1 == l1);

For reference type variables , The comparison is whether the addresses of the two objects are the same .

Integer i1 = new Integer(1);
Integer i2 = new Integer(1);
//  result ：false. adopt new establish , Point to two different objects in memory 
System.out.println(i1 == i2);

equals：Object Methods defined in class , It is usually used to compare whether the values of two objects are equal .

equals stay Object The method is actually equivalent to ==, But in actual use ,equals It is usually overridden to compare whether the values of two objects are the same .

Integer i1 = new Integer(1);
Integer i2 = new Integer(1);
//  result ：true. Two different objects , But with the same value 
System.out.println(i1.equals(i2));
 
// Integer Of equals Rewriting methods 
public boolean equals(Object obj) {
    if (obj instanceof Integer) {
        //  Are the values saved in the comparison object the same 
        return value == ((Integer)obj).intValue();
    }
    return false;
}

two-object hashCode() identical , be equals() It must be for true, Am I right? ？

incorrect .hashCode() and equals() The relationship is as follows ：

When there is a.equals(b) == true when , be a.hashCode() == b.hashCode() It must be true ,

In turn, , When a.hashCode() == b.hashCode() when ,a.equals(b) Not necessarily for true.