Integer

samples:

Integer x = 500;
Integer y = 500;
System.out.println(x == y + 0); //true
System.out.println(x == y); //false

Integer x = 127;
Integer y = 127;
System.out.println(x == y + 0); //true
System.out.println(x == y); //true

 

 

1.Integer + int :autounboxing 

  This is equivalent to :Integer.intValue() + int

2. Because of this code in Integer

public static Integer valueOf(int i) {
        if(i >= -128 && i <= IntegerCache.high)
            return IntegerCache.cache[i + 128];
        else
            return new Integer(i);
    }

Explanation:

Integer integer1 = 127 is a shortcut for Integer integer1 = Integer.valueOf(127), and for values between -128 and 127 (inclusive), the Integers are put in a cache and returned multiple times, while higher and lower numbers generate new Integers each time.