The difference between int and Integer

  1. Integer is a wrapper class for int, which is a basic data type in Java
  2. Integer variables must be instantiated before they can be used, whereas int variables do not
  3. An Integer is actually a reference to an object, and when you new an Integer, you’re actually generating a pointer to that object. Int stores data values directly
  4. The default value of Integer is null, and the default value of int is 0

Case 1

1Integer i = new Integer(100);

2Integer j = new Integer(100);

3System.out.print(i == j); //false

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Since an Integer variable is actually a reference to an Integer object, two Integer variables generated by new are never equal (because new generates two objects with different memory addresses).

Case 2

1Integer i = new Integer(100);

2int j = 100;

3System.out.print(i == j); //true

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If an Integer variable is compared with an int variable, the result will be true as long as the values of the two variables are equal.

Example 3

1Integer i = new Integer(100);

2Integer j = 100;

3System.out.print(i == j); //false

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Integer variables that are not generated by new are compared to variables generated by new Integer() and the result is false. Because:

  • When the value is between -128 and 127, non-new Integer variables refer to objects in the Java constant pool, while new Integer() variables refer to objects newly created in the heap, and they have different addresses in memory.
  • When the value of a variable is between -128 and 127, the Java API will eventually treat the variable as new Integer(I) (see item 4 below), and the address of the two intergers will also be different.)

Example 4

1Integer i = 100;

2Integer j = 100;

3System.out.print(i == j); //true

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1Integer i = 128;

2Integer j = 128;

3System.out.print(i == j); //false

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For two non-new generated Integer objects, the comparison result is true if the values of the two variables are in the range -128 to 127, and false if the values are not in the range