Examples name.concat(“hello”) - returns new string with hello on the end name.replace(“a”,“p”) - returns new string with all instances of a replaced with p name.toUpperCase() - returns uppercase version of string
string indexes start at 0 - string indexes end at length - 1 ( because they start at 0 ) str.charAt(1) - returns the character at index 1 name.length() - returns length of string name.substring(2, 6) - returns the substring beginning at 2 and ending at 5 ( this is just because it is exclude on second value ) if you do an index thats not available you get an indexoutofbounds exception
str.indexOf(j) - see what the index of a letter is in a string str1.equals(str2) - see if two strings have the same characters str.compareTo(str2) - compares the value of the first character thats not the same in both strings - is a numerical value based on that character being before or after the other character alphabetically ( really based on location in ascii table ) capitals are lower values than lowercase letters
Wrapper Classes
Some objects will only interact with other object datatypes ( e.g. arraylists ) We still want to store primitive values in arraylists we can use wrapper classes to do this
boolean = Boolean char = Character int = Integer double = Double
Wrapper classes are uppercase we only study Integer and Double Wrapper classes let primitive values do activities they could not normally do
Wrapper classes provide methods which are convenient Instantiation is the same as other objects Integer y = new Integer(30) datatype must match what you are trying to do ( i cant have a new Integer(30.4)) primitive types use lowercase letters Integer wrapper has a Integer.MIN_VALUE and Integer.MAX_VALUE and Integer.intValue
double wrapper has a Double.doubleValue
intValue does what you think it would do
so does doubleValue
autoboxing and unboxing autoboxing converts primitive int to an Integer or a primitive double to a Double it is done automatically by the java compiler instead of having to write the full constructor we can just write Integer myInt = 30
Java also autoboxes when a primitive value is passed as a parameter to a method that expects an object of the corresponding wrapper class
unboxing converts wrapper type to its corresponding primitive value done through just int myInt = myInteger