How to determine whether two Long objects are equal in Java?

Throw a question:

Long a = 4l;
Long b = 4l;
a == b //true

Long a = 128l;
Long b = 128l;
a == b //false

If the value of Long is between [-127,128], it is okay to use "==" to determine whether it is equal. If it is not in this range, you cannot use "==" ", the reason is explained in the source code as follows:

public static Long valueOf(long l) {
        final int offset = 128;
        if (l >= -128 && l <= 127) { // will cache
            return LongCache.cache[(int)l + offset];
        }
        return new Long(l);
    }

If it is not between [-127,128], a new object will be created. Naturally "==" two different objects, the result must be false.

Solution:

1. Use longValue() in Long for conversion

Long a = 128l;
Long b = 128l;
a.longValue() == b.longValue() //true

2. Use equals() in Long

Long a = 128l;
Long b = 128l;
a.equals(b);//true

Below This is the source code of this method:

public boolean equals(Object obj) {
        if (obj instanceof Long) {
            return value == ((Long)obj).longValue();
        }
        return false;
    }

Pitfalls in comparing two Long types

Generally speaking, "==" is enough to compare two basic data types. Long is rarely used. Type comparison.

But recently when I was writing a project, I encountered two Long type comparisons. At that time, I used double equals directly. However, when debugging, I found that when the code was executed to compare the two Long types, it did not enter the judgment body. , and then search for related issues online. It's actually very simple, but if you don't know, it's easy to fall into a trap.

The solution is as follows:

You can make two Long type variables call the ==longValue()== method respectively to achieve this.

Code:

Long a=...;
Long b=...;
if (a.longValue() == b.longValue()) {
             ...;
}

In fact, Long is a kind of java data packaging class. The above is the case where the packaging class Long is converted into the basic data type long. The following is a list of other data packaging classes that are unboxed and converted into In the case of basic data types:

Integer is converted to int, the intValue() method needs to be called

Double is converted to double, the doubleValue() method needs to be called

Float is converted to float , need to call floatValue() method

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