我在代码中使用以下组件：
我想确定这些部件是否使其效率更高或实际上减慢速度。任何其他建议也表示赞赏。
代码：
import java.lang.Math;
import java.util.*;
class Container{
public final byte[] binary_array;
private final int bit_length;
public Container(int nominal_bit_length){
int byte_length = (int)Math.ceil(nominal_bit_length / 8.0);
this.binary_array = new byte[byte_length];
this.bit_length = 8 * byte_length;
}
private String toBinaryString(int index){//convert into a binary string the byte value on which the bit number refered by the index exists
int byte_index = index / 8;
//System.out.println(index);
String str = Integer.toBinaryString(this.binary_array[byte_index]);
String formatted = ("00000000" + str).substring(str.length());
return formatted;
}
public char get(int index){
String str = this.toBinaryString(index);
return str.charAt(index % 8);//
}
public char set(int index, char value){
StringBuilder str = new StringBuilder(this.toBinaryString(index));
char temp = str.charAt(index % 8);//
str.setCharAt(index % 8, value);//
int byte_index = index / 8;
this.binary_array[byte_index] = (byte)Integer.parseUnsignedInt(str.toString(), 2);
return temp;
}
public int length(){
return this.bit_length;
}
public static Container preset(){
Container c = new Container(8);
c.set(1-1, '1');
c.set(4-1, '1');
c.set(6-1, '1');
c.set(8-1, '1');
return c;
}
}
class Screener{
private static void filterMultiplesOf(int num, Container container){
if (num == 1){
return;
}
int i = 2;
while ((i * num - 1) < container.length()){
container.set(i * num - 1, '1');
i++;
}
}
public static void filter(Container c){
int num = c.length();
if (num <= 8){
c = Container.preset();
} else{
Container base = new Container((int)Math.floor(Math.sqrt(num)));
filter(base);
for (int i = 0; i < base.length(); i++){
if (base.get(i) == '0'){
filterMultiplesOf(i+1, c);
}
}
}
}
}
public class Prime2{
public static void main(String[] args){
Scanner reader = new Scanner(System.in);
int num = reader.nextInt();
Container c = new Container(num);
Screener.filter(c);
for (int i = 1; i < c.length(); i++){
if (c.get(i) == '0'){
System.out.print((i + 1) + " ");
}
}
}
}
于12-03-2014编辑： 这段代码怎么样？
import java.util.*;
import java.util.stream.Collectors;
import java.util.stream.IntStream;
import java.util.stream.Stream;
public class PrimeGenerator {
public static Set<Integer> prime(int num){
if (num <= 2){
Set<Integer> foo = new HashSet<>();
foo.add(2);
return foo;
}
IntStream stream = IntStream.rangeClosed(1, num);
Set<Integer> base = prime((int)Math.ceil(Math.sqrt(num)));
IntStream multiples = base.stream().flatMapToInt((factor) -> (IntStream.rangeClosed(2, (int)Math.floorDiv(num, factor)).map(n -> n * factor)));
Set<Integer> primeset = stream.collect(HashSet::new, HashSet::add, HashSet::addAll);
Set<Integer> nonprimeset = multiples.collect(HashSet::new, HashSet::add, HashSet::addAll);
primeset.removeAll(nonprimeset);
primeset.remove(1);
return primeset;
}
public static void main(String[] args) {
// TODO code application logic here
prime(100000).stream().map(num -> num + " ").forEach(System.out::print);
}
}
以及：
import java.lang.Math;
import java.util.*;
/**
* Variation of BitSet which does NOT interpret the highest bit synonymous with
* its length.
*
* @author casper.bang@gmail.com
*/
class FixedBitSet extends BitSet{
int fixedLength;
public FixedBitSet(int fixedLength){
super(fixedLength);
this.fixedLength = fixedLength;
}
@Override
public int length() {
return fixedLength;
}
}
class Screener{
private static FixedBitSet preset;
static{
preset = new FixedBitSet(4);
preset.set(1-1, true);
preset.set(4-1, true);
}
private static void filterMultiplesOf(int num, FixedBitSet bitset){
//System.out.println("--------");
if (num == 1){
return;
}
int i = 2;
while ((i * num - 1) < bitset.length()){
bitset.set(i * num - 1, true);
i++;
}
}
public static void filter(FixedBitSet bitset){
//System.out.println("--------");
int num = bitset.length();
if (num <= 4){
//System.out.println("--------");
bitset = preset;
} else{
FixedBitSet base = new FixedBitSet((int)Math.floor(Math.sqrt(num)));
filter(base);
for (int i = 0; i < base.length(); i++){
if(!base.get(i)){
filterMultiplesOf(i + 1, bitset);
}
}
}
}
}
public class Prime3{
public static void main(String[] args){
Scanner reader = new Scanner(System.in);
int num = reader.nextInt();
FixedBitSet bs = new FixedBitSet(num);
// System.out.println(bs.length());
Screener.filter(bs);
for (int i = 1; i < bs.length(); i++){
if(!bs.get(i)){
System.out.print((i + 1) + " ");
}
}
}
}
答案 0 :(得分：1)
对字节数组的“高效”使用对代码的不良性能无关紧要，代码使用字符串构建来实现获取和设置。
而是编写使用低级位操作运算符（例如~，&和|）的代码来实现get和set
如果你不满意，那么考虑使用BitSet，这是一个JDK提供的类，用于相同的目的。
如果您想了解它是如何完成的，那么只需打开BitSet的源代码即可。