（1）
package com.example.multidownload;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.RandomAccessFile;
import android.os.Handler;
public class WriteThread extends Thread {
private String fileName;
private int startPosition;
private boolean state=true;
private int times;
private Handler handler;
public WriteThread(String fileName,int startPosition,Handler handler) {
super();
this.fileName=fileName;
this.startPosition=startPosition;
this.handler=handler;
}
@Override
public void run() {
super.run();
try {
RandomAccessFile randomAccessFile = new RandomAccessFile(fileName, "rwd");
randomAccessFile.seek(startPosition);
while (times<100) {
if(!state)
{
//java.lang.IllegalMonitorStateException: object not locked by thread before wait()
//即this.wait();周圍也要加鎖,不然會報上面的錯
synchronized (this) {
System.out.println(WriteThread.this.getName()+"線程等待中........"+times);
handler.sendEmptyMessage(0);
this.wait();
}
}
System.out.println(WriteThread.this.getName()+"線程執行中........"+times);
randomAccessFile.writeChars("hello:"+WriteThread.this.getName()+"="+times+"\r\n");
times++;
Thread.sleep(100);
}
handler.sendEmptyMessage(1);
randomAccessFile.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
public void pauseWrite()
{
this.state=false;
}
public void resumeWrite()
{
this.state=true;
//java.lang.IllegalMonitorStateException: object not locked by thread before notifyAll()
//即this.notifyAll();外圍也要加同步鎖,不然會報上面的錯
synchronized (this) {
this.notifyAll();
}
}
}
（2）
public class testThread {
/**
* @param 主/子線程同步,互斥打印(輪流打印10次,重複5變).............
*/
public static void main(String[] args) {
final Print print = new Print();
new Thread() {
public void run() {
for (int i = 0; i < 5; i++) {
print.printInSubThread(i);
}
};
}.start();
//主線程運行的代碼放在子線程後,不然打印了了一變就成睡眠狀態了，後面的代碼就運行不了
for (int i = 0; i < 5; i++) {
print.printInMainThread(i);
}
}
/////////////////////打印/////////////////////////
public static class Print {
private boolean isPrintMainThread = true;
public synchronized void printInMainThread(int rowNums) {
while (!isPrintMainThread) {
// 子線程在打印,等待
try {
this.wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
for (int i = 0; i < 10; i++) {
System.out.println("printInMainThread" + i + "/" + rowNums);
}
isPrintMainThread = false;
this.notify();
}
public synchronized void printInSubThread(int rowNums) {
while (isPrintMainThread) {
// 主線程在打印,等待
try {
this.wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
for (int i = 0; i < 10; i++) {
System.out.println("printInSubThread:" + i + "/" + rowNums);
}
isPrintMainThread = true;
this.notify();
}
}
}
（3）
如何避免多個線程同時下載同一張圖片(防止併發,要同步)?
final ReentrantLock reentrantLock = new ReentrantLock();
for (int i = 0; i < 10; i++) {
final int j=i;
new Thread(){
public void run() {
reentrantLock.lock();
System.out.println("hello:start:"+j);
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("hello:end:"+j);
reentrantLock.unlock();
};
}.start();
}
不同步(這樣就併發了,各做各的事).....................
final ReentrantLock reentrantLock = new ReentrantLock();
for (int i = 0; i < 10; i++) {
final int j=i;
new Thread(){
public void run() {
//reentrantLock.lock();
System.out.println("hello:start:"+j);
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("hello:end:"+j);
//reentrantLock.unlock();
};
}.start();
}
（4）
如何避免多個線程同時調用一個方法,導致數據混亂(防止併發,要同步)?
public class testSyn {
/**
* @param args
*/
public static void main(String[] args) {
new Thread(){
public void run() {
while (true) {
go("WUXIFU");
}
};
}.start();
new Thread(){
public void run() {
while (true) {
go("wuyaoping");
}
};
}.start();
}
private static /*synchronized*/void go(String s) {
for (int i = 0; i < s.length(); i++) {
System.out.print(s.charAt(i));
try {
Thread.sleep(10);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
System.out.println();
}
}
結果數據混亂(沒有在方法里加synchronized)：
在方法里加synchronized
public class testSyn {
/**
* @param args
*/
public static void main(String[] args) {
new Thread(){
public void run() {
while (true) {
go("WUXIFU");
}
};
}.start();
new Thread(){
public void run() {
while (true) {
go("wuyaoping");
}
};
}.start();
}
private static synchronized void go(String s) {
for (int i = 0; i < s.length(); i++) {
System.out.print(s.charAt(i));
try {
Thread.sleep(10);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
System.out.println();
}
}
結果正常:
(5)如何避免多線程請求同一個接口,只發送一次請求(只請求一次該接口)
package com.example.administrator.myapplication; import android.util.Log; import org.junit.Test; import java.lang.CloneNotSupportedException; import java.lang.Object; import java.lang.Override; import java.lang.System; import java.util.concurrent.locks.ReentrantLock; import static org.junit.Assert.*; /** * To work on unit tests, switch the Test Artifact in the Build Variants view. */ public class ExampleUnitTest { @Test public void addition_isCorrect() throws Exception { assertEquals(4, 2 + 2); test(); test002(); } private void test() { final ReentrantLock reentrantLock = new ReentrantLock(); for (int i = 0; i < 10; i++) { final int position = i; new Thread(){ @Override public void run() { super.run(); final int position2=position; // ReentrantLock reentrantLock2 = new ReentrantLock(); new Person(reentrantLock,position).sayHello(new Ihello() { public void goodBye() { System.out.println("成功了" + position2); } }); } }.start(); } } private void test002() { final ReentrantLock reentrantLock = new ReentrantLock(); final Person person = new Person(reentrantLock); for (int i = 10; i < 20; i++) { final int position = i; new Thread(){ @Override public void run() { super.run(); final int position2=position; person.sayHello(new Ihello() { public void goodBye() { System.out.println("成功了" + position2); } },position2); } }.start(); } } public interface Ihello { public void goodBye(); } public class Person { private int position; ReentrantLock reentrantLock; public Person(ReentrantLock reentrantLock, int position) { this.reentrantLock = reentrantLock; this.position = position; } public Person(ReentrantLock reentrantLock) { this.reentrantLock = reentrantLock; } public void sayHello(Ihello ihello) { reentrantLock.lock(); System.out.println("start" + position); ihello.goodBye(); System.out.println("end" + position); try { //TODO 所有在等待的同樣任務將全部取消 reentrantLock.lockInterruptibly(); } catch (InterruptedException e) { e.printStackTrace(); } reentrantLock.unlock(); System.out.println("結尾" + position); } public void sayHello(Ihello ihello,int position) { reentrantLock.lock(); System.out.println("start" + position); ihello.goodBye(); System.out.println("end" + position); try { //TODO 所有在等待的同樣任務將全部取消 reentrantLock.lockInterruptibly(); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println("結尾" + position); reentrantLock.unlock(); } } }
返回結果：
