for(int x=0; x<arr.length; x++) {System.out.println(arr[x]);
}
//foreach方法遍历更好用,还能用于集合的遍历：
for(object i:arr) {System.out.print(i);
}

方式1：for(int x=0; x<arr.length/2; x++) {int temp = arr[x];arr[x] = arr[arr.length-1-x];arr[arr.length-1-x] = temp;}
方式2：for(int start=0,end=arr.length-1; start<=end; start++,end--) {int temp = arr[start];arr[start] = arr[end];arr[end] = temp;}　　　　

public static String getString(String[] strArray,int index) {return strArray[index];
}

 public static int getIndex(int[] arr,int value) {int index = -1;for(int x=0; x<arr.length; x++) {if(arr[x] == value) {index = x;break;}}return index;(某值不存在，规定返回-1)
}

class Student {private String name;private int age;public Student(){}public Student(String name,int age) {this.name = name;this.age = age;}public String getName() {return name;}public void setName(String name) {this.name = name;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}
}

 class StudentDemo {public static void main(String[] args) {//方式1 (setXxx()方法，常用)Student s1 = new Student();s1.setName("林青霞");s1.setAge(27);System.out.println(s1.getName()+"---"+s1.getAge());//方式2  (带参构造方法，维护性较差)Student s2 = new Student("刘意",30);System.out.println(s2.getName()+"---"+s2.getAge());}
}

class Fu {}
class Zi extends Fu {}
Fu f = new Zi();

abstract class Fu {}
class Zi extends Fu {}
Fu f = new Zi();

interface Fu {}
class Zi implements Fu {}
Fu f = new Zi();

class Outer {private int num  = 10;public void method() {final int num2 = 20;注意这个在局部类外class Inner {public void show() {System.out.println(num);A:可以直接访问外部类的成员System.out.println(num2);}}Inner i = new Inner();B:在局部位置，可以创建内部类对象，通过i.show();对象调用内部类方法，来使用局部内部类功能}
}
class InnerClassDemo5 {public static void main(String[] args) {Outer o = new Outer();o.method();}
}   

interface Person {public abstract void study();
}
class PersonDemo {public void method(Person p) {p.study();}
}
class PersonTest {public static void main(String[] args) {PersonDemo pd = new PersonDemo();pd.method(new Person() {public void study() {System.out.println("好好学习，天天向上");}});}
}

              String s3 = new String("hello");String s4 = "hello";System.out.println(s3 == s4);// falseSystem.out.println(s3.equals(s4));// trueString s5 = "hello";String s6 = "hello";System.out.println(s5 == s6);// trueSystem.out.println(s5.equals(s6));// true

              String s1 = "hello";String s2 = "world";String s3 = "helloworld";System.out.println(s3 == s1 + s2);// falseSystem.out.println(s3.equals((s1 + s2)));// trueSystem.out.println(s3 == "hello" + "world");// true(这种比较现在方法区找，没有的话再在方法区里创建)System.out.println(s3.equals("hello" + "world"));// true

              boolean equals(Object obj)boolean equalsIgnoreCase(String str)boolean contains(String str)boolean startsWith(String str)boolean endsWith(String str)boolean isEmpty()

              int length()char charAt(int index)int indexOf(int ch)int indexOf(String str)int indexOf(int ch,int fromIndex)int indexOf(String str,int fromIndex)String substring(int start)String substring(int start,int end)

              byte[] getBytes()char[] toCharArray()static String valueOf(char[] chs)static String valueOf(int i)String toLowerCase()String toUpperCase()String concat(String str)

例：
Date d=new Date();
SimpleDateFormat sdf = new SimpleDateFormat("yyyy年MM月dd日 HH:mm:ss");
String s = sdf.format(d);

例：
String str = "2008-08-08 12:12:12";
//在把一个字符串解析为日期的时候，请注意格式必须和给定的字符串格式匹配
SimpleDateFormat sdf2 = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
Date dd = sdf2.parse(str);

如// 5年后的10天前c.add(Calendar.YEAR, 5);c.add(Calendar.DATE, -10);// 获取年year = c.get(Calendar.YEAR);// 获取月month = c.get(Calendar.MONTH);// 获取日date = c.get(Calendar.DATE);System.out.println(year + "年" + (month + 1) + "月" + date + "日");

如c.set(2011, 11, 11);// 获取年year = c.get(Calendar.YEAR);// 获取月month = c.get(Calendar.MONTH);// 获取日date = c.get(Calendar.DATE);System.out.println(year + "年" + (month + 1) + "月" + date + "日");

                  for(int x=0; x<list.size(); x++) {String s =(String) list.get(x);System.out.println(s);}

 例：   class Animal {}class Dog extends Animal {}   // 泛型如果明确的写的时候，前后必须一致Collection<Object> c1 = new ArrayList<Object>();// ?表示任意的类型都是可以的Collection<?> c7 = new ArrayList<Dog>();// ? extends E:向下限定，E及其子类Collection<? extends Animal> c11 = new ArrayList<Dog>();(Dog就是?)// ? super E:向上限定，E极其父类Collection<? super Animal> c13 = new ArrayList<Object>();(Object是Animal父类)Collection<? super Animal> c14 = new ArrayList<Animal>();(本身满足条件，向下同理)

public static int sum(int... a) {int s = 0;for(int x : a){s +=x;}return s;
}

public class Student implements Comparable<Student> {}//泛型要写对应的类@Override//然后重写接口方法，具体情况根据需求来写，下面只是个例子public int compareTo(Student s) {// 主要条件 姓名的长度int num = this.name.length() - s.name.length();// 姓名的长度相同，不代表姓名的内容相同int num2 = num == 0 ? this.name.compareTo(s.name) : num;// 姓名的长度和内容相同，不代表年龄相同，所以还得继续判断年龄int num3 = num2 == 0 ? this.age - s.age : num2;return num3;
}

　　　　　　　　　　  　 // 如果一个方法的参数是接口，那么真正要的是接口的实现类的对象// 而匿名内部类就可以实现这个东西TreeSet<Student> ts = new TreeSet<Student>(new Comparator<Student>() {@Overridepublic int compare(Student s1, Student s2) {// 姓名长度int num = s1.getName().length() - s2.getName().length();// 姓名内容int num2 = num == 0 ? s1.getName().compareTo(s2.getName()): num;// 年龄int num3 = num2 == 0 ? s1.getAge() - s2.getAge() : num2;return num3;}});

                     Map<String,String> hm = new HashMap<String,String>();hm.put("it002","hello");hm.put("it003","world");hm.put("it001","java");//方式1 键找值Set<String> set = hm.keySet();for(String key : set) {String value = hm.get(key);System.out.println(key+"---"+value);}//方式2 键值对对象找键和值Set<Map.Entry<String,String>> set2 = hm.entrySet();for(Map.Entry<String,String> me : set2) {String key = me.getKey();String value = me.getValue();System.out.println(key+"---"+value);}

(带参要super(message);)
public class Teacher {public void check(int score) throws MyException {if (score > 100 || score < 0) {throw new MyException("分数必须在0-100之间");} else {System.out.println("分数没有问题");}}
// 针对MyException继承自RuntimeException，这个就不用throws// public void check(int score) {// if (score > 100 || score < 0) {// throw new MyException();// } else {// System.out.println("分数没有问题");// }// }
}

String[] sss=f4.list(new FilenameFilter() {@Overridepublic boolean accept(File dir, String name) {File f=new File(dir,name);boolean flag=f.isFile();boolean flag2=f.getName().endWith(".java");return flag&&flag2;  //或return new File(dir,name).isFile()&&name.endsWith(".java");}
});

           FileInputStream fis = new FileInputStream("fos.txt");//方式1int by = 0;while((by=fis.read())!=-1) {System.out.print((char)by);}//方式2byte[] bys = new byte[1024];int len = 0;while((len=fis.read(bys))!=-1) {System.out.print(new String(bys,0,len));}fis.close();

　　　　FileInputStream fis=new FileInputStream("d:\\t.txt");FileOutputStream fos=new FileOutputStream("d:\\a.txt");int by=0;while((by=fis.read())!=-1){fos.write(by);}fis.close();fos.close();    

       BufferedReader br = new BufferedReader(new FileReader("a.txt"));PrintWriter pw = new PrintWriter(new FileWriter("b.txt"),true);String line = null;while((line=br.readLine())!=null) {pw.println(line);}pw.close();br.close();

　　　　// 构造方法ThreadGroup(String name)       ThreadGroup tg = new ThreadGroup("这是一个新的组");MyRunnable my = new MyRunnable();// Thread(ThreadGroup group, Runnable target, String name)Thread t1 = new Thread(tg, my, "林青霞");Thread t2 = new Thread(tg, my, "刘意");

// 创建一个线程池对象，控制要创建几个线程对象。
// public static ExecutorService newFixedThreadPool(int nThreads)
ExecutorService pool = Executors.newFixedThreadPool(2);
// 可以执行Runnable对象或者Callable对象代表的线程
pool.submit(new MyRunnable());
pool.submit(new MyRunnable());
//结束线程池
pool.shutdown();

实例如下：public class Student {// 构造私有private Student() {}// 自己造一个/ 静态方法只能访问静态成员变量，加静态// 为了不让外界直接访问修改这个值，加privateprivate static Student s = new Student();// 提供公共的访问方式// 为了保证外界能够直接使用该方法，加静态public static Student getStudent() {return s;}}

实例如下：public class Teacher {private Teacher() {}private static Teacher t = null;public synchronized static Teacher getTeacher() {if (t == null) {t = new Teacher();}return t;}
}

实例如下：public static void main(String[] args) throws IOException {Runtime r = Runtime.getRuntime();//r.exec("winmine");// r.exec("notepad");// r.exec("calc");//r.exec("shutdown -s -t 10000");r.exec("shutdown -a");}