在下面的示例中,锁定是在实例变量employee上获得的(不在此),但在进入synchronized块时,TestClass1的Threads仍然被锁定.任何建议为什么这种行为.据我所知,如果它同步就应该被锁定.
public class TestClass{
public static void main(String args[]){
TestClass1 obj = new TestClass1();
Thread t1 = new Thread(obj, "T1");
Thread t2 = new Thread(obj, "T2");
t1.start();
t2.start();
}
}
class TestClass1 implements Runnable{
Employee employee = new Employee();
public void myMethod () {
synchronized (employee) {
try {
Thread.sleep(4000L);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
public void myOtherMethod() {
synchronized (employee) {
try {
Thread.sleep(4000L);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
@Override
public …我正在努力自学java,在使用类编写代码时遇到了这个错误
Exception in thread "main" java.util.NoSuchElementException
at java.util.Scanner.throwFor(Unknown Source)
at java.util.Scanner.next(Unknown Source)
at java.util.Scanner.nextDouble(Unknown Source)
at StateCalculator.getOperand(StateCalculator.java:29)
at StateCalculator.main(StateCalculator.java:77)
以下是我的代码:
import java.util.Scanner;
public class StateCalculator {
private double currentValue = 0;
//Initialize to 0
public StateCalculator() {
}
public static int displayMenu() {
Scanner keyboard = new Scanner(System.in);
int menuChoice = 0;
do {
System.out.print("Menu\n 1. Add\n 2. Subtract\n 3. Multiply\n 4. Divide\n 5.Clear\n 6. Quit\n What would you like to do?: ");
menuChoice = keyboard.nextInt();
} while(menuChoice < 1 …我已经实现了Singleton类,如下所示:
public class Singleton {
private static Singleton instance = null;
private Singleton() {
}
private synchronized static void createInstance() {
instance = new Singletone();
}
public static Singleton getInstance() {
if(instance == null){
createInstance();
}
return instance;
}
}
但我想知道它是否是单例的正确实现.多线程环境中是否有任何问题.
我正在为我的"java简介"编程课程做一个代码,我遇到了一个错误,我真的不知道如何修复.我一直有错误说:
unreported exception java.io.FileNotFoundException; must be caught or declared to be thrown
Scanner fileIn = new Scanner(hours);
这是代码:
import java.util.Scanner;
import java.io.File;
public class program2{
public static void main(String[] args) {
int[][] array = new int [8][7];
int[] total = new int [array.length];
int[] finalTotal = new int[array.length];
int[] employees = {0,1,2,3,4,5,6,7};
File hours = new File("prog2.dat"); //read file
Scanner fileIn = new Scanner(hours);//assign hours to array
while(fileIn.hasNext()){
for(int i = 0; i < 8; i++) {
for (int a …有几次我遇到过for-each循环会导致问题的情况,包括异常和崩溃,而for(it=list.iterator;it.hasNext();)没有任何问题.这包括修改集合(我知道不应该为每个集合发生,但不知道为什么)以及我克隆东西的其他情况.不记得任何具体的例子,我只是想到了它.
for-each只是我指向的第二个循环类型的快捷方式吗？有人可以解释那里的差异究竟是什么？
我想对一个字符串使用两种方法,就像这样
outputLabel.setText(firstname.charAt(0) + toLowerCase());
如何让它在特定位置返回字符并将字符串转换为小写？
我希望输出是单个字符,转换为小写,并在一行上.
非常感谢!
我正在尝试开发一个客户端,使用自定义协议与生物识别设备进行通信,但似乎没有任何效果.我正在使用MessageToByteEncoder和MessageToByteDecoder来处理输入和输出数据:
public class PacketDecoder extends ByteToMessageDecoder {
@Override
protected void decode(ChannelHandlerContext context, ByteBuf input, List<Object> out) throws Exception {
System.out.println("readable bytes: " + input.readableBytes());
if (input.readableBytes() >= 1) {
if (input.getByte(0) != DataCodes.START_BYTE) {
input.readByte();
return;
}
}
if (input.readableBytes() >= 3) {
byte command = input.getByte(2);
boolean extendedLenght = (command & 0x80) == 0x80;
short dataLength;
int headerLength;
if (extendedLenght) {
byte[] dataLengthBytes = new byte[2];
input.getBytes(3, dataLengthBytes);
dataLength = Utils.getShort(dataLengthBytes);
headerLength = 5;
} else {
dataLength = …用于生成基于正则表达式的随机字符串的Java代码.我试过generex库,但它没有提供准确的输出.例如:
Generex generex = new Generex("^[6-9]\\d{9}$");
System.out.println(generex.random());
输出是:^ 8677547981 $,而我期望输出为8677547981.似乎generex无法处理像"^","$"等特殊字符.
有人可以帮忙吗？
for(int i=0; i< n; i++) {
hashMap.put("Name",name.get(i));
hashMap.put("Website",website.get(i));
}
我想迭代地向HashMap添加多个值我希望我的输出是这样的
我如何添加到hashmap,我没有得到预期的结果.