Primitive Types and Methods. Reference Types and Methods. Review: Methods and Reference Types

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Caitlin Page
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Primitive Types and Methds Java uses what is called pass-by-value semantics fr methd calls When we call a methd with input parameters, the value f that parameter is cpied and passed alng, nt the

Changing the value f the input parameter desn t change the riginal value back at the calling lcatin, it nly changes the cpied value Class #39: Reference Types and Methds, Lping Algrithms Sftware

1 Primitive Types and Methds Java uses what is called pass-by-value semantics fr methd calls When we call a methd with input parameters, the value f that parameter is cpied and passed alng, nt the riginal Fr primitive types, the values are actual numbers, characters, bleans, etc. Changing the value f the input parameter desn t change the riginal value back at the calling lcatin, it nly changes the cpied value Class #39: Reference Types and Methds, Lping Algrithms Sftware Design I (CS 120): M. Allen, 08 Nvember 18 int i = 5; methd2( i ); System.ut.println( i ); private vid methd2( int num ) num = num + 5; System.ut.println( num ); Prints: 5 2 Review: Methds and Reference Types Nte: if yu input an array and change its elements in a methd, the riginal will be changed in the prcess Arrays behave like reference type bjects: making changes t the bject referred t by the input variable can change the riginal Nt true fr primitives: changes t input dn t affect riginal v.setsize( 10, 10 ); Reference Types and Methds v.setsize( 10, 10 ); 3 4 1

2 Reference Types and Methds Reference Types and Methds v.setsize( 10, 10 ); v.setsize( 10, 10 ); In this case, nly ne bject exists, and we are changing it directly. Thus, we have nly ne width value t Oval( 0, 0, 10, 10 ) v v 5 6 Reference Types and Methds One thing t watch ut fr: fr reference types, the thing we pass as input is a cpy f the reference (address) Changing the cpied reference itself des nt change the riginal We can nly change the riginal bject by actually using the reference and changing things abut the bject that is there Reference Types and Methds v = new Oval( 0, 0, 10, 10 ); Prints: 5 v = new Oval( 0, 0, 10, 10 Oval( 0, 0, 5, 5 ) 7 8 2

3 Reference Types and Methds v = new Oval( 0, 0, 10, 10 ); S far, this is just the same (nly ne bject). Reference Types, and Methds v = new Oval( 0, 0, 10, 10 ); This versin nw creates a whle new bject (withut changing the riginal). We nw have tw separate width values t print. v v Oval( 0, 0, 10, 10 ) 9 10 Develping an Algrithm As the prblems we slve get harder, it pays t wrk ut what we want t d in a systematic manner Think f the cde yu write as a set f step-by-step directins An algrithm: 1. Starts smewhere (the input, r ther starting cnditins) 2. Fllws instructins, each f which is clear and unambiguus 3. When dne, have the result we want (utput r end cnditins) Often helps t lay ut the cde befre yu write it Write ut what yu want t d as a set f instructins Explain it in English (r whatever natural language yu want) Translate what yu want t d int Java (r whatever prgramming language yu want t use) Searching an Array Suppse yu want t find smething in an array Given series f Strings, want t find ne particular String Or find a particular integer, in a series f integers Or a duble in a series f dubles, etc. A basic thing we might d with data in a database, wrds in a dcument, search terms in an index f web-pages [0] [1] [2]... [l-3] [l-2] [l-1] A B C... D E F Hw wuld yu explain hw t d this t smene?

A Simple Methd fr Searching Cnsider hw t explain search prcess in simple step-by-step English Islating the Lgical Structure Take yur English translatin and try t islate the basic mving parts 1.

4 A Simple Methd fr Searching Cnsider hw t explain search prcess in simple step-by-step English Islating the Lgical Structure Take yur English translatin and try t islate the basic mving parts 1. Start at the beginning f the list [0] [1] [2]... [l-3] [l-2] [l-1] A B C... D E F 3a. If it is, then yu fund it! Reprt it & stp. 1. Start at the beginning f the list 2. Check if it is what we are lking fr 3a. If it is, then yu fund it! Reprt it & stp. Repetitin: a lp Cnditinal: if/else 2. Check if it is what yu are lking fr 3b. If it is nt, and yu are nt at the end f list, repeat prcess n the next entry. 4. If yu get t the end f the list, and haven t fund it, it isn t there. Reprt & stp. 3b. If it is nt, and yu are nt at the end f list, repeat prcess n the next entry. 4. If yu get t the end f the list, and haven t fund it, it isn t there. Reprt & stp. Output: return statement Translating int Java Once yu have the mving parts, yu can translate int cde; Repetitin private blean searcharray( String[] arr, String s ) blean fund = false; int i = 0; while ( i < arr.length ) if ( s.equals( arr[i] ) ) Cnditinal fund = true; i++ ; return fund; Is this the best translatin? What happens if the array is very large? Is this efficient? Can it be made mre efficient? Output 15 A Mre Efficient Translatin This versin f the algrithm nw stps as sn as it finds its target Repetitin private blean searcharray( String[] arr, String s ) int i = 0; while ( i < arr.length ) if ( s.equals( arr[i] ) ) Cnditinal return true; i++; return false; A cmmn trick: since the methd will stp and return true if we ever see a match, the last line can simply return false (If we ever get t last line, n match is fund) Output 16 4

5 This Week & Next Meetings this week: Tuesday Thursday: regular classrm Friday: in the CS Lab (16 Wing) Midterm 2: next Tuesday (13 Nvember) Practice Exam n D2L nw (key t fllw) Reading: due next Wednesday (14 Nv.) Office Hurs: Wing 210 Mnday/Wednesday/Friday, 12:00 PM 1:00 PM Tuesday/Thursday, 1:30 PM 3:00 PM 17 5

LAB 7 (June 29/July 4) Structures, Stream I/O, Self-referential structures (Linked list) in C

LAB 7 (June 29/July 4) Structures, Stream I/O, Self-referential structures (Linked list) in C Due: July 9 (Sun) 11:59 pm 1. Prblem A Subject: Structure declaratin, initializatin and assignment. Structure