1. import java.util.*; 2. 3. Class FindStuff { 4. public static void main(String [] args) { 5. // insert code here 6. c.put("x", 123); 7. } 8. } 分别插入到第5行,哪三行允许代码编译?()
1. import java.util.*; 2. class SubGen { 3. public static void main(String [] args) { 4. //insert code here 5. } 6. } class Alpha { } class Beta extends Alpha { } class Gamma extends Beta { } 和四段代码片段: s1. ArrayList〈? extends Alpha〉 list1 = new ArrayList〈Gamma〉(); s2. ArrayList〈Alpha〉 list2 = new ArrayList〈? extends Alpha〉(); s3. ArrayList〈? extends Alpha〉 list3 = new ArrayList〈? extends Beta〉(); s4. ArrayList〈? extends Beta〉 list4 = new ArrayList〈Gamma〉(); ArrayList〈? extends Alpha〉 list5 = list4; 哪些片段分别插入到第4行,可允许代码编译?()
import java.util.*; public class PQ { public static void main(String[] args) { PriorityQueue pq = new PriorityQueue(); pq.add(”carrot”); pq.add(”apple”); pq.add(”banana”); System.out.println(pq.poll() +”:” + pq.peek()); } } What is the result?()
import java.util.*; public class LetterASort { public static void main(String[] args) { ArrayList strings = new ArrayList(); strings.add(‟aAaA”); strings.add(”AaA”); strings.add(‟aAa”); strings.add(”AAaa”); Collections.sort(strings); for (String s: strings) { System.out.print(s + “ “); } } } What is the result?()
import java.util.*; class KeyMaster { public int i; public KeyMaster(int i) { this.i = i; } public boolean equals(Object o) { return i == ((KeyMaster)o).i; } public int hashCode() { return i; } } public class MapIt { public static void main(String[] args) { Set set = new HashSet(); KeyMaster k1 = new KeyMaster(1); KeyMaster k2 = new KeyMaster(2); set.add(k1); set.add(k1); set.add(k2); set.add(k2); System.out.print(set.size() + “:”); k2.i = 1; System.out.print(set.size() + “:”); set.remove(k1); System.out.print(set.size() + “:”); set.remove(k2); System.out.print(set.size()); } } What is the result?()
import java.util.*; public class NameList { private List names = new ArrayList(); public synchronized void add(String name) { names.add(name); } public synchronized void printAll() { for (int i = 0; i System.out.print(names.get(i) +“ “); } } public static void main(String[] args) { final NameList sl = new NameList(); for(int i=0;i<2;i++) { new Thread() { public void ruin() { sl.add(”A”); sl.add(”B”); sl.add(”C”); sl.printAll(); } }.start(); } } } Which two statements are true if this class is compiled and run?()
import java.util.*; public class WrappedString { private String s; public WrappedString(String s) { this.s = s; } public static void main(String[] args) { HashSet hs = new HashSet(); WrappedString ws1 = new WrappedString(”aardvark”); WrappedString ws2 = new WrappedString(”aardvark”); String s1 = new String(”aardvark”); String s2 = new String(”aardvark”); hs.add(ws1); hs.add(ws2); hs.add(s1); hs.add(s2); System.out.println(hs.size()); } } What is the result?()
import java.util.*; class ScanStuff { public static void main(String [] args) { String s = "x,yy,123"; Scanner sc = new Scanner(s); while (sc.hasNext()) System.out.print(sc.next() + " "); } } 结果是什么?()
1. import java.util.*; 2. public class Example { 3. public static void main(String[] args) { 4. // insert code here 5. set.add(new integer(2)); 6. set.add(new integer(l)); 7. System.out.println(set); 8. } 9. } Which code, inserted at line 4, guarantees that this program will output [1,2]? ()
1. import java.util.*; 2. class ForInTest { 3. static List list = new ArrayList(); 4. 5. static List getList() { return list; } 6. 7. public static void main(String [] args) { 8. list.add("a"); list.add("b"); list.add("c"); 9. // insert code here 10. System.out.print(o); 11. } 12. } 第 9 行插入哪一项将输出 abc?()