How to call method before the constructor (this(...)) . Refer to https://stackoverflow.com/questions/285177/how-do-i-call-one-constructor-from-another-in-java

Call_Static_Method_In_Constructor.java

// Normally in order to call constructor from another constructor, we have to call it from the first line (Java rule)
// Example:

public class MyInteger extends Integer {
    private int myIntNumber;
    
    public MyInteger() {
        this(0);
    }
    
    public MyInteger(int num) {
        this(num, 1);
    }
    
    public MyInteger(int num, int multiple) {
        this.myIntNumber = num * multiple;
    }
}
// It is also considered preferrable to call from smallest constructor to the largest
// Also, because of this rule, we can only chain ONE constructor inside another, that means something like below is illegal
    public MyInteger() {
        this(0);
        this(1, 2);
    }

// or
    public MyInteger() {
        super();
        this(0);
    }

// However, in some rare cases that we truly need to do some stuff before calling another constructor (I could not think of one, though)
// We could do that using static method, like this:

public class MyInteger extends Integer {
    private int myIntNumber;
    
    public MyInteger() {
        this(0);
    }
    
    // Here we can call the absOf() static method to get the absolute value before calling the multiply constructor
    public MyInteger(int num) {
        this(absOf(num), 1);
    }
    
    public MyInteger(int num, int multiple) {
        this.myIntNumber = num * multiple;
    }
    
    private static int absOf(int num) {
        // Note: Math.abs(Integer.MIN_VALUE) will return the most negative number instead of the positive 
        // because signed integer runs from (-2147483648 ~ 2147483647) so there is no 2147483648
        return num >= 0 ? num : (num == Integer.MIN_VALUE ? num : Math.abs(num));
    }
}

// Although, it is considered a bad design, and I suggest that the designer should take time and rethink about it