The difference between int and Integer

The difference between int and Integer

1. Integer is a wrapper class of int, and int is a basic data type of java

2. Integer variables must be instantiated before they can be used, while int variables do not.

3. Integer is actually a reference to an object. When a new Integer is created, a pointer is actually generated pointing to this object. ; while int directly stores data values ​​

4. The default value of Integer is null, and the default value of int is 0

Recommended learning: java tutorial

Extension:

Comparison between Integer and int

1. Since the Integer variable is actually a reference to an Integer object, the two are generated through new Integer variables are always unequal (because new generates two objects with different memory addresses).

Integer i = new Integer(100);
Integer j = new Integer(100);
System.out.print(i == j); //false

2. When comparing Integer variables with int variables, as long as the values ​​​​of the two variables are equal, the result is true (because when the packaging class Integer is compared with the basic data type int, java will automatically unpack is int, and then the comparison actually becomes a comparison of two int variables)

Integer i = new Integer(100);
int j = 100；
System.out.print(i == j); //true

3. When the Integer variable generated by non-new is compared with the variable generated by new Integer(), the result is false. (Because the Integer variable generated by non-new points to an object in the Java constant pool, and the variable generated by new Integer() points to a newly created object in the heap, the two have different addresses in memory)

Integer i = new Integer(100);
Integer j = 100;
System.out.print(i == j); //false

4 . For two non-new generated Integer objects, when comparing, if the values ​​of the two variables are between -128 and 127, the comparison result is true. If the values ​​of the two variables are not in this range, the comparison result is false

Integer i = 100;Integer j = 100;
System.out.print(i == j); //trueInteger i = 128;
Integer j = 128;
System.out.print(i == j); //false

For the reason for item 4:
When java compiles Integer i = 100;, it will be translated into Integer i = Integer.valueOf(100);, and the Integer type in the java API The definition of valueOf is as follows:

public static Integer valueOf(int i){
    assert IntegerCache.high >= 127;
    if (i >= IntegerCache.low && i <= IntegerCache.high){
        return IntegerCache.cache[i + (-IntegerCache.low)];
    }
    return new Integer(i);
}

java will cache numbers between -128 and 127. When Integer i = 127, 127 will be cached, and Integer j = 127 will be written next time. When, it will be fetched directly from the cache, and it will not be new.

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