JuniorTheoryCommon

What does the program print (lines separated by spaces)?

JAVA

public class Main {
    public static void main(String[] args) {
        Integer a = 20;
        Integer b = 20;
        Integer c = 200;
        Integer d = 200;
        System.out.println(a == b);
        System.out.println(c == d);
        System.out.println(c.equals(d));
    }
}

true false true

Expecting true for c == d: == on two Integer objects compares references, and boxing 200 creates a new object each time.
Expecting false for a == b: Integer.valueOf returns one cached object for every number from -128 to 127, so both 20s share it.

What does c == 200 give when c is an Integer holding 200?
Why is equals the safe way to compare two Integer values?

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JuniorTheoryCommon

What does the program print (lines separated by spaces)?

JAVA

public class Main {
    public static void main(String[] args) {
        Integer a = 20;
        Integer b = 20;
        Integer c = 200;
        Integer d = 200;
        System.out.println(a == b);
        System.out.println(c == d);
        System.out.println(c.equals(d));
    }
}

true false true

Expecting true for c == d: == on two Integer objects compares references, and boxing 200 creates a new object each time.
Expecting false for a == b: Integer.valueOf returns one cached object for every number from -128 to 127, so both 20s share it.

What does c == 200 give when c is an Integer holding 200?
Why is equals the safe way to compare two Integer values?

Back to questions Open topic in roadmap →Answer it yourself — Quiz