1。写2个线程对j加1,2个线程对j减1
public class ThreadTest {
public int j;
public static void main(String[] args) {
ThreadTest t = new ThreadTest();
D d1 = new D(t);
D d2 = new D(t);
E e1 = new E(t);
E e2 = new E(t);
d1.run();
d2.run();
e1.run();
e2.run();
}
}
class D implements Runnable {
private ThreadTest t;
public D(ThreadTest t){
this.t = t;
}
public void run() {
t.j –;
// System.out.println(t.j);
}
}
class E implements Runnable{
private ThreadTest t;
public E(ThreadTest t){
this.t = t;
}
public void run(){
t.j ++;
// System.out.println(t.j);
}
}
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2.写一个单例
//懒汉式public class Singleton {
public static Singleton instance = null; private Singleton() {}
public static Singleton getInstance() {
if(instance == null)
instance = new Singleton();
return instance; }}
//饿汉式public class Singleton {
public static Singleton instance = new Singleton();
private Singleton() {}
public static Singleton getInstance() { return instance; }}
3.读取一个文件，将每一行存入linkedlist中，然后倒序取出显示
public class FileReader {
public static void main(String[] args) {
File f = new File("1.txt");
LinkedList<String> list = new LinkedList<String>();
try {
java.io.FileReader fr = new java.io.FileReader(f);
java.io.BufferedReader br = new BufferedReader(fr);
String s = null;
try {
while ((s = br.readLine())!= null){
list.add(s);
}
} catch (IOException e) {
e.printStackTrace();
}
} catch (FileNotFoundException e) {
e.printStackTrace();
}
for(int i = 0 ; i < list.size(); i++){
System.out.println(list.get(list.size() – i -1));
}
}
}
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数据库
学生表（Student）
name course score
张三 英语 81
张三 数学 90
。。。。。
问题一：用一条sql读出每门课程分数都高于80分的学生name