Javase 基礎中必須要掌握的19個程式設計
阿新 • • 發佈：2018-11-09
1.陣列的逆序
public void getReverse1(int[]arr) {
int start=0;
int end=arr.length-1;
for(int i=0;i<arr.length/2;i++) {
int temp=arr[start];
arr[start]=arr[end];
arr[end]=temp;
start++;
end--;
}
}
public void getReverse2(int 2.陣列的查詢
public int search(int[]arr,int num) {
for(int i=0;i<arr.length;i++) {
if(num==arr[i]) {
return i;
}
}
return 3.陣列的遍歷
public void printArr1(int [] arr) {
for (int i : arr) {
System.out.println(i);
}
}
public void printArr2(int[] arr) {
for(int i=0;i<arr.length;i++) {
System.out.println(arr[i]);
}
}4.陣列的最值
public void getMaxandMin0(int [] arr) {
int max=arr[0 5.氣泡排序
public void bubbleSort(int[] arr) {
for(int i=0;i<arr.length-1;i++) {
for(int j=0;j<arr.length-1-i;j++) {
if(arr[j]>arr[j+1]) {
int temp=arr[j];
arr[j]=arr[j+1];
arr[j+1]=temp;
}
}
}
System.out.println(Arrays.toString(arr));
}6.選擇排序
public void selecSort(int [] arr) {
for(int i=0;i<arr.length-1;i++) {
for(int j=i+1;j<arr.length;j++) {
if(arr[i]>arr[j]) {
int temp=arr[i];
arr[i]=arr[j];
arr[j]=temp;
}
}
}
System.out.println(Arrays.toString(arr));
}7.二分查詢
//二分查詢前提是陣列是有序的,所以開始需要對陣列進行排序
public void binarySearch(int[] arr,int num) {
int start=0;
int end=arr.length-1;
while(start<=end) {
int middleIndex=(start+end)/2;
int middle=arr[middleIndex];
if(arr[0]<arr[arr.length-1]) {//判斷陣列為升序還是降序
if(num==middle) {
System.out.println(num+"所在陣列中的索引是:"+middleIndex);
return;
}else if(num>middle) {
start=middleIndex+1;
}else {
end=middleIndex-1;
}
}else {
if(num==middle) {
System.out.println(num+"所在陣列中的索引是:"+middleIndex);
return;
}else if(num>middle) {
end=middleIndex-1;
}else {
start=middleIndex+1;
}
}
}
System.out.println("對不起,陣列中不存在該數");
}8.單例設計模式的寫法
//餓漢式
class Hungry{
private static Hungry h=new Hungry();
private Hungry() {
}
public static Hungry getInstance() {
return h;
}
}
//懶漢式
class Lazy{
private static Lazy l=null;
private Lazy() {
}
public static Lazy getInstance() {
if(l==null) {
l=new Lazy();
}
return l;
}
}9.遞迴查詢檔案
public void searchFiles(String path,String suffix) {
//將路徑包裝成File類
File file = new File(path);
//判斷資料夾或檔案
if(file.isFile()&&(file.getAbsolutePath().toLowerCase().endsWith(suffix)) ) {//如果是檔案
System.out.println(file.getAbsolutePath());
}else {//如果是資料夾,獲取其內容
File[] files = file.listFiles();
if(files!=null&&files.length>0) {
for (File f : files) {//遍歷內容後 , 遞迴呼叫方法
searchFiles(f.getAbsolutePath(), suffix);
}
}
}
}10.遞迴刪除檔案
public void deleteFiles(String path) {
/**
* 刪除檔案, java中資料夾裡有內容,無法刪除該資料夾, 空資料夾就是檔案
*/
//將路徑包裝成類, 然後判斷是否為資料夾,然後刪除
File file = new File(path);
if(file.isFile()) {
file.delete();
}else {
File[] files = file.listFiles();
if(files!=null&&files.length>0) {
for (File f : files) {
deleteFiles(f.getAbsolutePath());
}
}
file.delete();//之後把自己刪除
}
}
11.Map的遍歷
public void mapBianli(Map<Integer,String> map) {
Set<Entry<Integer, String>> entrySet = map.entrySet();
Iterator<Entry<Integer, String>> iterator = entrySet.iterator();
//使用迭代器
while(iterator.hasNext()) {
Entry<Integer, String> next = iterator.next();
System.out.println(next.getKey()+next.getValue());
}
//使用增強for迴圈
for (Entry<Integer, String> entry : entrySet) {
System.out.println(entry.getKey()+entry.getValue());
}
//利用keySet列印
Set keySet = map.keySet();
for (Object key : keySet) {
System.out.println("key:"+key +", value"+map.get(key));
}
}12.使用迭代器完成對集合的遍歷
public void iteratorList(List list) {
Iterator it = list.iterator();
while(it.hasNext()) {
System.out.println(it.next());
}
}13.如何呼叫成員變數和靜態變數
* 成員變數使用物件名呼叫
* 靜態變數使用類名呼叫
14.如何實現定義一個介面，並實現
public interface A{
public void show();
}
public class SubInstance implements A{
public void show(){
System.out.println("葫蘆娃,葫蘆娃,一根藤上七個瓜")
}
}15.匿名內部類的寫法
匿名內部類指的是 實現了一個介面,或是繼承了一個(抽象) 類的 子類物件;
格式:
new 介面/(抽象)類名 ( ){重新寫的方法};
new A(){
public void eat(){
sysout("長生不老藥何在?")
}
}.eat();
或者:
A a=new A(){
public void eat(){
sysout("長生不老藥何在?")
};
--------------
new A() {
public void show() {
System.out.println("我是賣報的小行家");
}
}.show();
A a=new A() {
@Override
public void show() {
System.out.println("我是匿名內部類的第二種書寫方式 ");
}
};16.分別使用Comparable和Comparator實現對Person類的排序（規則自定）
public static void main(String[] args) {
List<Person> list = new ArrayList<Person>();
list.add(new Person("葫蘆娃",10,95));
list.add(new Person("哪吒",5,96));
list.add(new Person("鐵膽火車俠",5,93));
list.add(new Person("藤吉少爺",9,99));
/**
* 使用 Comparable 對Person類進行排序 ,需要Person 類實現 Comparator<泛型 Person型別> 介面
* 然後 方法重寫, 按照實現 方式進行設計
*/
Collections.sort(list,new Person());
for (Person person : list) {
System.out.println(person);
}
---------------------------------------------
/**
* 使用 Comparator 實現對person類的排序
* 使用介面的匿名內部類,(list,new Comparator<Person>() {方法重寫});
*/
Collections.sort(list, new Comparator<Person>() {
@Override
public int compare(Person o1, Person o2) {
//年齡升序排列,如果年齡相同,那麼成績將序排列
if(o1.getAge()==o2.getAge()) {
return o2.getScore()>o1.getScore()?1:-1;
}
return o1.getAge()-o2.getAge();
}
});
Iterator<Person> it = list.iterator();
while(it.hasNext()) {
System.out.println(it.next());
}
---------------------------------------------
//使用lambda表示式
Collections.sort(list, (o1,o2)->{
if(o1.getAge()==o2.getAge()) {
return o2.getScore()>o1.getScore()?1:-1;
}
return o1.getAge()-o2.getAge();
});
Iterator<Person> it2 = list.iterator();
while(it2.hasNext()) {
System.out.println(it2.next());
}17.UDP資料的傳輸
Thread thread = new Thread(client);
Thread thread2 = new Thread(server);
thread2.start();
Thread.sleep(200);
thread.start();
------------------------
new Thread(new Server()).start();
Thread.sleep(200);
new Thread(new Client()).start();
class Client implements Runnable{
@Override
public void run() {
try {
DatagramSocket ds=new DatagramSocket();
DatagramPacket dp = new DatagramPacket("峰巒如聚,波濤如怒,山河表裡潼關路".getBytes(),
"峰巒如聚,波濤如怒,山河表裡潼關路".getBytes().length , InetAddress.getLocalHost(), 8686);
ds.send(dp);
ds.close();
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
class Server implements Runnable{
public void run() {
try {
DatagramSocket ds=new DatagramSocket(8686);
DatagramPacket dp = new DatagramPacket(new byte[64*1024],64*1024);
ds.receive(dp);
byte[] data = dp.getData();
int length = dp.getLength();
InetAddress address = dp.getAddress();
System.out.println(address.getHostAddress()+"+++"+new String(data,0,length));
ds.close();
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
18.TCP建立連線並傳輸資料（多層資料夾）
class TcpClient implements Runnable{
public void run() {
try {
Socket s= new Socket("127.0.0.1", 1991);
BufferedInputStream bis = new BufferedInputStream(new FileInputStream("c:/users/gaopu/desktop/P70621-081006-1.png"));
BufferedOutputStream bos = new BufferedOutputStream(s.getOutputStream());
byte[] bs=new byte[1024];
int len;
while((len=bis.read(bs))!=-1) {
bos.write(bs,0,len);
}
bos.flush();
bos.close();
s.close();
} catch (Exception e) {
e.printStackTrace();
}
}
}
class TcpServer implements Runnable{
public void run() {
try {
ServerSocket ss= new ServerSocket(1991);
Socket s = ss.accept();
System.out.println("已連線");
BufferedInputStream bis = new BufferedInputStream(s.getInputStream());
BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream("c:/users/gaopu/desktop/拷貝副本.png"));
byte[] bs=new byte[1024];
int len;
while((len=bis.read(bs))!=-1) {
bos.write(bs,0,len);
}
bos.flush();
bos.close();
System.out.println("已接收");
s.close();
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}19.多執行緒買票程式
Thread thread1 = new Thread(new Tickets(),"視窗1" );
Thread thread2 = new Thread(new Tickets(),"視窗2" );
Thread thread3 = new Thread(new Tickets(),"視窗3" );
thread1.start();
thread2.start();
thread3.start();
class Tickets implements Runnable{
static int tickets=100;
public void run() {
ReentrantLock lock = new ReentrantLock();
while(true) {
lock.lock();
try {
Thread.sleep(10);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
if(tickets>0) {
System.out.println("第"+Thread.currentThread().getName()+
"個視窗正在售第"+ tickets-- +"張票");
}else {
break;
}
lock.unlock();
}
}