OCP 17 Exam - chapter 4 notes

Chapter 4 notes

• be aware that exam want to trick us on concatenation of String and numbers, e.g. prints 66

      int five = 5;
      String six = "6";
      System.out.println(1 + five + six);

• String#substring accepts numbers/indexes from 0 to length of String, e.g.

var text = "abcdef";
System.out.println(text.substring(0, 6)); // prints abcdef
System.out.println(text.substring(6, 6)); // prints ""
// System.out.println(text.substring(0, 7)); // throws java.lang.StringIndexOutOfBoundsException

• equals and hashcode is not required on exam, but be aware that if equals is implemented then both should be consistent to avoid collisions in “hash” based collections
• String#contains is just convenience method instead string.indexOf(otherString) != -1
• String#trim removes only ` \t\n\r, but String#strip removes also Unicode whitespace, e.g. \u2000`
• String#ident … TODO

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Playground code

https://github.com/RG9/rg-playground-ocp17/blob/main/Chapter4.java