操作系统-磁盘调度算法:先来先服务,最短寻道时间优先,scan算法

1.先来先服务

public class FCFS {

/**
* 磁盘调度:先来先服务
*/
private static int startPosition = 100 ;//磁头开始位置
private static int totalMoving = 0;
private static List<Integer> visitList = new ArrayList<Integer>();//访问磁道列表
public static void main(String[] args) {
System.out.println("------磁盘调度:先来先服务算法模拟---------");
input();
running();
display();
}
//接收用户输入列表
public static void input(){
System.out.print("请输入磁道访问列表,以空格分开:");
Scanner sc = new Scanner(System.in);
String input = sc.nextLine();
String[] inputList = input.split("\\s");
try{
for(String in : inputList){
visitList.add(Integer.valueOf(in));
}
}
catch(Exception e){
System.out.println("输入的必须是数字,请重新开始！！！");
System.exit(1);
}
}

//运行
public static void running(){
Iterator<Integer> it = visitList.listIterator();
int thisPosition = 0;
while(it.hasNext()){
thisPosition = it.next();
totalMoving += Math.abs(startPosition-thisPosition);
startPosition = thisPosition;
System.out.println("当前访问磁道号:"+thisPosition);
}
}
public static void display(){
System.out.println("平均寻道时间是:"+(double)totalMoving/visitList.size());
}

}

2.最短寻道时间优先

public class SSTF {

/**
*磁盘调度:最短寻道时间优先
*/
private static int startPosition = 100 ;//磁头开始位置
private static int totalMoving = 0;
private static List<Integer> visitList = new LinkedList<Integer>();//访问磁道列表
private static int size;
public static void main(String[] args) {
System.out.println("------磁盘调度:最短寻道时间优先算法模拟---------");
input();
running();
display();

}

//接收用户输入列表
public static void input(){
System.out.print("请输入磁道访问列表,以空格分开:");
Scanner sc = new Scanner(System.in);
String input = sc.nextLine();
String[] inputList = input.split("\\s");
try{
for(String in : inputList){
visitList.add(Integer.valueOf(in));
}
size = visitList.size();
}
catch(Exception e){
System.out.println("输入的必须是数字,请重新开始！！！");
System.exit(1);
}
}

//运行
public static void running(){
int visitNumber = 0;
for(int i=0,size = visitList.size();i<size;i++){
visitNumber = searchMinimum(startPosition);
System.out.println("当前访问磁道:"+visitNumber);
}
}
//寻找与当前磁头最近的磁道号
public static int searchMinimum(int startPosition){
int min = Integer.MAX_VALUE,index = 0,i = 0,thisPosition = 0,computering=0;
Iterator<Integer> it = visitList.iterator();
while(it.hasNext()){
int in = it.next();
computering = Math.abs(startPosition-in);//判断是否小于最小值
if(min>computering){
index = i;
min = computering;
}
i++;
}
thisPosition = visitList.remove(index);//设置当前磁头，访问后移除
totalMoving += Math.abs(startPosition-thisPosition);

SSTF.startPosition = thisPosition;

return thisPosition;
}
public static void display(){
System.out.println("平均寻道时间是:"+(double)totalMoving/size);
}

}

3.SCAN算法

public class SCAN {

/**
* 磁盘调度:scan算法
*/
private static int startPosition = 100 ;//磁头开始位置
private static int totalMoving = 0;
private static List<Integer> visitList = new ArrayList<Integer>();//访问磁道列表
private static int moveDirection = 0;//0:向外移动,1:向里移动
private static int size;
public static void main(String[] args) {
System.out.println("------磁盘调度:scan算法模拟---------");
input();
running();
display();
}

//接收用户输入列表
public static void input(){
System.out.print("请输入磁道访问列表,以空格分开:");
Scanner sc = new Scanner(System.in);
String input = sc.nextLine();
String[] inputList = input.split("\\s");
try{
for(String in : inputList){
visitList.add(Integer.valueOf(in));
}
size = visitList.size();
}
catch(Exception e){
System.out.println("输入的必须是数字,请重新开始！！！");
System.exit(1);
}
}

//运行
public static void running(){
int visitNumber = 0;
for(int i=0,size = visitList.size();i<size;i++){
visitNumber = searchMinimum(startPosition);
System.out.println("当前访问磁道:"+visitNumber);
}
}
//寻找与当前磁头最近并且和磁头的移动方向一致的磁道号
public static int searchMinimum(int startPosition){
int min = Integer.MAX_VALUE,index = -1,i = 0,thisPosition = 0,computing=0;
Iterator<Integer> it = visitList.iterator();
while(it.hasNext()){
int in = it.next();
computing = Math.abs(startPosition-in);
if((min>computing)&&(moveDirection==0)&&(in>startPosition)){//向外移动
index = i;
min = computing;
}
else if((min>computing)&&(moveDirection==1)&&(in<startPosition)){//向里移动
index = i;
min = computing;
}
if((index == -1)&&(moveDirection == 0)){//若移动到尽头,则返回扫描
moveDirection = 1;
}
else if((index == -1)&&(moveDirection == 1)){
moveDirection = 0;
}
i++;
}
thisPosition = visitList.remove(index);//设置当前磁头，访问后移除
totalMoving += Math.abs(startPosition-thisPosition);

SCAN.startPosition = thisPosition;

return thisPosition;
}
public static void display(){
System.out.println("平均寻道时间是:"+(double)totalMoving/size);
}

}