1. Strings & Arrays CSCI-1302
Lakshmish Ramaswamy

2. Organizational Matters
Tutor hours
Tuesday 6:00 – 7:00 PM; 306 GSRC
Wednesday 6:00 – 7:40; 306 GSRC
Office hours
Will be ed to you today
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3. The “==“ Operator
For reference types “==“ operator returns true only if
They refer to the same object
They are null
Button a = new Button (“yes”);
Button b = new Button (“yes”);
Button c = a;
c==a returns true where as b==a returns false
Observe that semantics is consistent with reference concept

4. Strings Handled through the String reference type
Permits operator overloading
But not a primitive type
Immutable – may not be changed after assignment
Safe to use “=“ operator
String empty = “”;
String message = “Hello”;
String repeat = message;
Value of repeat can be changed by creating a new String object

5. String Concatenation
Java does not allow operator overloading for reference types
“+” is the only exception for strings
+ performs concatenations of lhs and rhs and returns reference to newly constructed String object
Left associative
“a” + “b”
“b” + 5
5 + “c”
“a”
“a”

6. String Comparisons <, >, <=, >= not defined
== and != have semantics identical to reference types
String lhs = new String(“CSCI 1302”);
String rhs = “CSCI String(“CSCI 1302”);
lhs == rhs returns false
Equals method for testing equality
lhs.equals(rhs) returns true
compareTo for lexicographic comparison

7. String Methods String temp = “CSCI1302” int len = temp.length();
char ch = temp.charAt(2);
String subtemp = temp.substring(1, 4)

8. More on Arrays Array of reference types Button [ ] arrayofButtons;
arrayofButtons = new Button [5];
for (int i = 0; i < arrayofButtons.length(); i ++){
arrayofButtons[i] = new Button(); }
arrayofButton[4].setLabel(“No”);

9. Dynamic Array Expansion
int [] arr = new int [10];
…….
// But you actually need array of 12 integers
int[ ] original = arr;
arr = new int[12];
for(int i = 0; i < 10; i ++)
arr[i] = original[i]
original = null;

10. Illustration

13. ArrayList Built in functionality for dynamic sized arrays
Size and capacity
add method increases size by 1 & adds new item at the given position
Expands the size if the capacity is reached
get method for retrieving object at particular index

15. Multidimensional Arrays
Multidimensional arrays are actually array of arrays
int [ ][ ] x = new int [2][3];
\\ x is a an array of two arrays, x[0] and x[1]
x.length(); \\ answer is 2
x[0].length(); \\ answer is 3;
x[1].length(); \\ answer is 3;

16. Ragged Arrays