A. s.add(2) B. s.add(new Integer(2)) C. s.add(“2”) D. s.add(new java.util.Date())
public class Demo{ public static void main(String[] args){ List al = new ArrayList(); al.add(“1”); al.add(“2”); al.add(“2”); al.add(“3”); System.out.println(al); } } 上述程序執(zhí)行后的輸出是哪項(xiàng)?()
A. [1,2,3] B. [1,2,2,3] C. [1,2,3,3] D. [2,1,3,2]
程序員正在進(jìn)行一個(gè)項(xiàng)目,必須實(shí)現(xiàn)equals方法與所給的hashCode方法協(xié)調(diào)運(yùn)行:() public int hashCode() { return (size.hashCode() + color.hashCode()) * 17; } 哪一個(gè)equals方法支持此目標(biāo)?()
A. 無法確定 B. public boolean equals(Object o) { Sock s = (Sock) o;return size.equals(s.size); } C. public boolean equals(Object o) { Sock s = (Sock) o;return color.equals(s.color); } D. public boolean equals(Object o) { Sock s = (Sock) o;return size.equals(s.size) &&color.equals(s.color); }