Revisão OCPJP7 - Class Design (parte 01)

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Revisão OCPJP7 - Class Design (parte 01) - Questões e Respostas

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Revisão OCPJP7 - Class Design (parte 01)

  1. 1. OCPJP Objetivo: Java Class Design
  2. 2. Questão Dado: package com.sun.scjp; public class Geometry { public static final double DIAMETER = 0.72; // kilometers } Quais 2 podem acessar o membro DIAMETER corretamente da classe Geometry? (Escola 2 opções) A. import com.sun.scjp.Geometry; public class Ground { public double halfway { return Geometry.DIAMETER/2.0; } } B. import static com.sun.scjp.Geometry; public class Ground { public double halfway { return DIAMETER/2.0; } } C. import static com.sun.scjp.Geometry.*; public class Ground { public double halfway { return DIAMETER/2.0; } } D. package com.sun.scjp; public class Ground { public double halfway { return DIAMETER/2.0; } }
  3. 3. Questão Resolvida Dado: package com.sun.scjp; public class Geometry { public static final double DIAMETER = 0.72; // kilometers } Quais 2 podem acessar o membro DIAMETER corretamente da classe Geometry? (Escola 2 opções) A. import com.sun.scjp.Geometry; public class Ground { public double halfway { return Geometry.DIAMETER/2.0; } } B. import static com.sun.scjp.Geometry; public class Ground { public double halfway { return DIAMETER/2.0; } } C. import static com.sun.scjp.Geometry.*; public class Ground { public double halfway { return DIAMETER/2.0; } } D. package com.sun.scjp; public class Ground { public double halfway { return DIAMETER/2.0; } } Correto Correto
  4. 4. Questão As classes abaixo estão definidas em 2 arquivos separados 1. package processors; 2. public class ByteProcessor { 3. public static void process(byte[] b) { /* more code here */ } 4. } 1. package apps; 2. public class ByteApp { 3. public static void main(String[] args) { 4. byte[] bytes = new byte[256]; 5. // insert code here 6. } 7. } O que é necessário na linha 5 da classe ByteApp para usar o método da classe ByteProcessor? a. process(bytes); b. ByteProcessor.process(bytes); c. processors.ByteProcessor.process(bytes); d. ByteApp cannot use methods in ByteProcessor. e. import processors.ByteProcessors.*; process(bytes);
  5. 5. Questão Resolvida As classes abaixo estão definidas em 2 arquivos separados 1. package processors; 2. public class ByteProcessor { 3. public static void process(byte[] b) { /* more code here */ } 4. } 1. package apps; 2. public class ByteApp { 3. public static void main(String[] args) { 4. byte[] bytes = new byte[256]; 5. // insert code here 6. } 7. } O que é necessário na linha 5 da classe ByteApp para usar o método da classe ByteProcessor? a. process(bytes); b. ByteProcessor.process(bytes); c. processors.ByteProcessor.process(bytes); d. ByteApp cannot use methods in ByteProcessor. e. import processors.ByteProcessors.*; process(bytes); Correto
  6. 6. Questão As classes abaixo estão definidas em 2 arquivos separados 1. package processors; 2. public class ByteProcessor { 3. private static void process(byte[] b) { /* more code here */ } 4. } 1. package apps; 2. public class ByteApp { 3. public static void main(String[] args) { 4. byte[] bytes = new byte[256]; 5. // insert code here 6. } 7. } What is required at line 5 in class ByteApp to use the process method of ByteProcessor? a. process(bytes); b. ByteProcessor.process(bytes); c. apps.ByteProcessor.process(bytes); d. processors.ByteProcessor.process(bytes); e. import processors.ByteProcessor.*; process(bytes); f. ByteApp cannot use the process method in ByteProcessor.
  7. 7. Questão Resolvida As classes abaixo estão definidas em 2 arquivos separados 1. package processors; 2. public class ByteProcessor { 3. private static void process(byte[] b) { /* more code here */ } 4. } 1. package apps; 2. public class ByteApp { 3. public static void main(String[] args) { 4. byte[] bytes = new byte[256]; 5. // insert code here 6. } 7. } What is required at line 5 in class ByteApp to use the process method of ByteProcessor? a. process(bytes); b. ByteProcessor.process(bytes); c. apps.ByteProcessor.process(bytes); d. processors.ByteProcessor.process(bytes); e. import processors.ByteProcessor.*; process(bytes); f. ByteApp cannot use the process method in ByteProcessor. Correto
  8. 8. Questão Um desenvolvedor está criand a classe Book, que necessita de acessar a classe Paper. A classe Paper encontra-se em um arquivo JAR chamado myLib.jar. Quais 3 dos abaixo que usados independentemente permitirão ao desenvolvedor usar a classe Paper ao compilar a classe Book? (Escolha três opções.) a. The JAR file is located at $JAVA_HOME/jre/classes/myLib.jar. b. The JAR file is located at $JAVA_HOME/jre/lib/ext/myLib.jar. c. The JAR file is located at /foo/myLib.jar and a classpath environment variable is set that includes /foo/myLib.jar/Paper.class. d. The JAR file is located at /foo/myLib.jar and a classpath environment variable is set that includes /foo/myLib.jar. e. The JAR file is located at /foo/myLib.jar and the Book class is compiled using javac - cp/foo/myLib.jar/Paper Book.java. f. The JAR file is located at /foo/myLib.jar and the Book class is compiled using javac -d/foo/myLib.jar Book.java g. The JAR file is located at /foo/myLib.jar and the Book class is compiled using javac -classpath /foo/myLib.jar Book.java
  9. 9. Questão Resolvida Um desenvolvedor está criand a classe Book, que necessita de acessar a classe Paper. A classe Paper encontra-se em um arquivo JAR chamado myLib.jar. Quais 3 dos abaixo que usados independentemente permitirão ao desenvolvedor usar a classe Paper ao compilar a classe Book? (Escolha três opções.) a. The JAR file is located at $JAVA_HOME/jre/classes/myLib.jar. b. The JAR file is located at $JAVA_HOME/jre/lib/ext/myLib.jar. c. The JAR file is located at /foo/myLib.jar and a classpath environment variable is set that includes /foo/myLib.jar/Paper.class. d. The JAR file is located at /foo/myLib.jar and a classpath environment variable is set that includes /foo/myLib.jar. e. The JAR file is located at /foo/myLib.jar and the Book class is compiled using javac - cp/foo/myLib.jar/Paper Book.java. f. The JAR file is located at /foo/myLib.jar and the Book class is compiled using javac -d/foo/myLib.jar Book.java g. The JAR file is located at /foo/myLib.jar and the Book class is compiled using javac -classpath /foo/myLib.jar Book.java Correto Correto Correto
  10. 10. Questão Dado: 1. package com.apps; 2. 3. public class MyApp { 4. public static void main(String[] args) {} 5. } And MyApp exists in the /programs/com/apps directory. Assume the CLASSPATH environment variable is set to "." (current directory). Quais 2 comandos java irão executar MyApp? (Escolha 2 opções) A. java MyApp if run from the /programs directory B. java com.apps.MyApp if run from the /programs directory C. java -classpath /programs com.apps.MyApp if run from any directory D. java -classpath . MyApp if run from the /programs/com/apps directory E. java -classpath /programs/com/apps:. MyApp if run from the /programs directory F. java com.apps.MyApp if run from the /programs/com/apps directory
  11. 11. Questão Resolvida Dado: 1. package com.apps; 2. 3. public class MyApp { 4. public static void main(String[] args) {} 5. } And MyApp exists in the /programs/com/apps directory. Assume the CLASSPATH environment variable is set to "." (current directory). Quais 2 comandos java irão executar MyApp? (Escolha 2 opções) A. java MyApp if run from the /programs directory B. java com.apps.MyApp if run from the /programs directory C. java -classpath /programs com.apps.MyApp if run from any directory D. java -classpath . MyApp if run from the /programs/com/apps directory E. java -classpath /programs/com/apps:. MyApp if run from the /programs directory F. java com.apps.MyApp if run from the /programs/com/apps directory Correto Correto
  12. 12. Questão 1. import java.util.*; 2. public class MapTest 3. { 4. public static void main(String[] args) 5. { 6. Object obj = new LinkedHashMap(); 7. if(obj instanceof Collection) 8. System.out.print("For "); 9. if(obj instanceof Map) 10. System.out.print("A Few "); 11. if(obj instanceof LinkedList) 12. System.out.print("Dollars More "); 13. if(obj instanceof HashMap) 14. System.out.print("Good Men"); 15. } 16. } O que irá acontecer quando vocÊ tentar compilar e rodar o código acima? a. It will print - A Few Good Men b. It will print - For A Few Good Men c. It will print - For A Few Dollars More Good Men d. It will print - For A Few Dollars More e. It will print - For A Few f. It will print - A Few Dollars More
  13. 13. Questão Resolvida 1. import java.util.*; 2. public class MapTest 3. { 4. public static void main(String[] args) 5. { 6. Object obj = new LinkedHashMap(); 7. if(obj instanceof Collection) 8. System.out.print("For "); 9. if(obj instanceof Map) 10. System.out.print("A Few "); 11. if(obj instanceof LinkedList) 12. System.out.print("Dollars More "); 13. if(obj instanceof HashMap) 14. System.out.print("Good Men"); 15. } 16. } O que irá acontecer quando vocÊ tentar compilar e rodar o código acima? a. It will print - A Few Good Men b. It will print - For A Few Good Men c. It will print - For A Few Dollars More Good Men d. It will print - For A Few Dollars More e. It will print - For A Few f. It will print - A Few Dollars More Correto
  14. 14. Questão Se o código abaixo exibe: count = 3, qual das declarações abaixo é false? (Assumindo que os métodos equals() e hashCode() foram sobrescritos corretamente). 1. int count = 1; 2. if(a.equals(b)) 3. count++; 4. if(c.equals(d)) 5. count++; 6. if(a.hashCode() == b.hashCode()) 7. count++; 8. if(c.hashCode() == d.hashCode()) 9. count++; 10. System.out.println("count = " + count); a. a.equals(b) and !(c.equals(d)) b. a.equals(b) or c.equals(d) but not both c. a.hashCode()==b.hashCode() and c.hashCode() == d.hashCode() d. a.equals(b) and c.equals(d)
  15. 15. Questão Resolvida Se o código abaixo exibe: count = 3, qual das declarações abaixo é false? (Assumindo que os métodos equals() e hashCode() foram sobrescritos corretamente). 1. int count = 1; 2. if(a.equals(b)) 3. count++; 4. if(c.equals(d)) 5. count++; 6. if(a.hashCode() == b.hashCode()) 7. count++; 8. if(c.hashCode() == d.hashCode()) 9. count++; 10. System.out.println("count = " + count); a. a.equals(b) and !(c.equals(d)) b. a.equals(b) or c.equals(d) but not both c. a.hashCode()==b.hashCode() and c.hashCode() == d.hashCode() d. a.equals(b) and c.equals(d) Correto
  16. 16. Questão O que irá acontecer ao tentar compilar e executar o código abaixo? 1. public final class EqualsDemo 2. { 3. private String str; 4. 5. public EqualsDemo(String s) 6. { 7. str = s; 8. } 9. 10. public boolean equals(EqualsDemo obj) 11. { 12. if(!(obj instanceof EqualsDemo)) 13. return false; 14. EqualsDemo ed = (EqualsDemo)obj; 15. return (str == ed.str || (str != null && str.equals(ed.str))); 16. } 17. 18. public static void main(String[] args) 19. { 20. EqualsDemo demo1 = new EqualsDemo("Java"); 21. EqualsDemo demo2 = new EqualsDemo("java"); 22. System.out.println(demo1.equals(demo2)); 23. } 24. } A. It will print - true B. It will print - false C. Compilation error D. Exception
  17. 17. Questão Resolvida O que irá acontecer ao tentar compilar e executar o código abaixo? 1. public final class EqualsDemo 2. { 3. private String str; 4. 5. public EqualsDemo(String s) 6. { 7. str = s; 8. } 9. 10. public boolean equals(EqualsDemo obj) 11. { 12. if(!(obj instanceof EqualsDemo)) 13. return false; 14. EqualsDemo ed = (EqualsDemo)obj; 15. return (str == ed.str || (str != null && str.equals(ed.str))); 16. } 17. 18. public static void main(String[] args) 19. { 20. EqualsDemo demo1 = new EqualsDemo("Java"); 21. EqualsDemo demo2 = new EqualsDemo("java"); 22. System.out.println(demo1.equals(demo2)); 23. } 24. } A. It will print - true B. It will print - false C. Compilation error D. Exception Correto
  18. 18. Questão Como você implementaria do método hashCode() corretamente para a classe abaixo? (Assumindo que essa classe implemnta o método equals() corretamente e use a implementação mais apropriada) public class HashDemo { private Integer arr[]; //other methods not shown } A. public int hashCode() { int hash = 7; if(arr == null) hash = 31 * hash + 0; else for(int i=0; i<arr.length; i++) { hash = 31 * hash +(arr[i] == null? 0 : arr[i].hashCode()); } return hash; } B. public int hashCode() { int hash = 7; if(arr == null) hash = 31 * hash + 0; else for(int i=0; i<arr.length; i++) { hash = 31 * hash + arr[i].hashCode(); } return hash; } C. public int hashCode() { int hash = 7; if(arr == null) hash = 31 * hash + 0; else hash = 31 * hash + arr.hashCode(); return hash; } D. The array should not be involved in the calculation of the hashCode() method.
  19. 19. Questão Ressolvida Como você implementaria do método hashCode() corretamente para a classe abaixo? (Assumindo que essa classe implemnta o método equals() corretamente e use a implementação mais apropriada) public class HashDemo { private Integer arr[]; //other methods not shown } A. public int hashCode() { int hash = 7; if(arr == null) hash = 31 * hash + 0; else for(int i=0; i<arr.length; i++) { hash = 31 * hash +(arr[i] == null? 0 : arr[i].hashCode()); } return hash; } B. public int hashCode() { int hash = 7; if(arr == null) hash = 31 * hash + 0; else for(int i=0; i<arr.length; i++) { hash = 31 * hash + arr[i].hashCode(); } return hash; } C. public int hashCode() { int hash = 7; if(arr == null) hash = 31 * hash + 0; else hash = 31 * hash + arr.hashCode(); return hash; } D. The array should not be involved in the calculation of the hashCode() method. Correto
  20. 20. Questão Dado: 2. public class foo { 3. void m1() { } 4. protected void m2 { } 5. } 6. class bar extends foo { 7. // insert code here 8. } Quais fragmentos de código, inseridos independentemente na linha 7 irão compilar? (Escolha 4) A. public void m1() { } B. protected void m1() { } C. private void m1() { } D. void m2() { } E. public void m2() { } F. protected void m2() { } G. private void m2() { }
  21. 21. Questão Resolvida Dado: 2. public class foo { 3. void m1() { } 4. protected void m2 { } 5. } 6. class bar extends foo { 7. // insert code here 8. } Quais fragmentos de código, inseridos independentemente na linha 7 irão compilar? (Escolha 4) A. public void m1() { } B. protected void m1() { } C. private void m1() { } D. void m2() { } E. public void m2() { } F. protected void m2() { } G. private void m2() { } Correto Correto Correto Correto

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