Java5新特性及使用

public interface Map<K,V> {

    V get(Object key);

    V put(K key, V value);

}

Map<Integer, String> map = new HashMap<Integer, String>();

public class GenericMethods {

    //当方法操作的引用数据类型不确定的时候，可以将泛型定义在方法上
    public <T> void f(T x){
        System.out.println(x.getClass().getName());
    }

    public static void main(String[] args) {
        GenericMethods gm = new GenericMethods();
        gm.f(99);
        gm.f("abc");
    }

}

public class GenericVarargs {

    public static <T> List<T> makeList(T... args) {
        List<T> result = new ArrayList<T>();
        for(T item:args) {
            result.add(item);
        }
        return result;
    }

    public static void main(String[] args) {
        List ls = makeList("A");
        System.out.println(ls);
        ls = makeList("A","B","C");
        System.out.println(ls);
        ls = makeList("ABCDEFGHIJKLMNOPQRSTUVWXYZ".split(""));
        System.out.println(ls);
    }

}

public class ErasedTypeEquivalence {

    public static void main(String[] args) {
        Class c1 = new ArrayList<String>().getClass();
        Class c2 = new ArrayList<Integer>().getClass();
        System.out.println(c1 == c2); // 输出true.
    }

}

class Building {

}

class House extends Building {

}

public class ClassTypeCapture<T> {

    Class<T> kind;

    public ClassTypeCapture(Class<T> kind) {
        this.kind = kind;
    }

    public boolean f(Object arg) {
        return kind.isInstance(arg);
    }

    public static void main(String[] args) {
        ClassTypeCapture<Building> ctt1 = new ClassTypeCapture<Building>(Building.class);
        System.out.println(ctt1.f(new Building())); // true
        System.out.println(ctt1.f(new House())); // true
        ClassTypeCapture<House> ctt2 = new ClassTypeCapture<House>(House.class);
        System.out.println(ctt2.f(new Building())); // false
        System.out.println(ctt2.f(new House())); // true
    }
}

int[] integers = {1, 2, 3, 4};
/* 开始遍历 */
for (int i : integers) {
    System.out.println(i);/* 依次输出“1”、“2”、“3”、“4” */
}

ArrayList<Integer> intList = new ArrayList<Integer>();
intList.add(1); //自动装箱
intList.add(2); // 自动装箱

int number = intList.get(0); // 自动拆箱

public class AutoboxingTest {

    public static void main(String args[]) {
        // 示例 1: 使用'=='号进行原始类型的比较(没有自动装箱)
        int i1 = 1;
        int i2 = 1;
        System.out.println("i1==i2 : " + (i1 == i2)); // true

        // 示例 2: 使用'=='号进行原始类型和对象类型混合的比较(自动装箱)
        Integer num1 = 1;
        int num2 = 1;
        System.out.println("num1 == num2 : " + (num1 == num2)); // true

        // 示例 3: 使用'=='号进行Integer对象类型的比较(会有缓存的特殊情况)
        Integer obj1 = 127; // 自动装箱将调用`Integer.valueOf()`且缓存该对象，以便重用
        Integer obj2 = 127; // 获取已经缓存过的对象
        System.out.println("obj1 == obj2 : " + (obj1 == obj2)); // true

       // 示例 4: 使用'=='号进行Integer对象类型的比较(不会缓存)
        Integer obj3 = 128; // 自动装箱将调用`Integer.valueOf()`不缓存该对象
        Integer obj4 = 128; // 同样是自动装箱将调用`Integer.valueOf()`
        System.out.println("obj3 == obj4 : " + (obj3 == obj4)); // false

        // 示例 5: 使用'=='号进行`new`出来的新`Integer`对象类型的比较
        Integer one = new Integer(1); // no autoboxing
        Integer anotherOne = new Integer(1);
        System.out.println("one == anotherOne : " + (one == anotherOne)); // false
    }

}

i1==i2 : true
num1 == num2 : true
obj1 == obj2 : true
obj3 == obj4 : false
one == anotherOne : false

/**
 * Cache to support the object identity semantics of autoboxing for values between
 * -128 and 127 (inclusive) as required by JLS.
 *
 * The cache is initialized on first usage.  The size of the cache
 * may be controlled by the {@code -XX:AutoBoxCacheMax=<size>} option.
 * During VM initialization, java.lang.Integer.IntegerCache.high property
 * may be set and saved in the private system properties in the
 * sun.misc.VM class.
 */
private static class IntegerCache {
    static final int low = -128;
    static final int high;
    static final Integer cache[];

    static {
        // high value may be configured by property
        int h = 127;
        String integerCacheHighPropValue =
            sun.misc.VM.getSavedProperty("java.lang.Integer.IntegerCache.high");
        if (integerCacheHighPropValue != null) {
            try {
                int i = parseInt(integerCacheHighPropValue);
                i = Math.max(i, 127);
                // Maximum array size is Integer.MAX_VALUE
                h = Math.min(i, Integer.MAX_VALUE - (-low) -1);
            } catch( NumberFormatException nfe) {
                // If the property cannot be parsed into an int, ignore it.
            }
        }
        high = h;

        cache = new Integer[(high - low) + 1];
        int j = low;
        for(int k = 0; k < cache.length; k++)
            cache[k] = new Integer(j++);

        // range [-128, 127] must be interned (JLS7 5.1.7)
        assert IntegerCache.high >= 127;
    }

    private IntegerCache() {}
}

private static Integer count;

//NullPointerException on unboxing
if (count <= 0) {
    System.out.println("Count is not started yet");
}

print(String... args) {
   // 方法代码
}

print(String... args) {
    for(String temp:args) {
        System.out.println(temp);
    }
}

print();
print("hello");
print("hello","lisi");

double r = Math.cos(Math.PI * theta);

import static java.lang.Math.*;

double r = cos(PI * theta);

class PBDemo {

    public static void main(String args[]) {
        try {
            ProcessBuilder proc = new ProcessBuilder("notepad.exe", "testfile");
            proc.start();
        } catch (Exception e) {
            System.out.println("Error executing notepad.");
        }
    }

}

import java.io.BufferedReader;
import java.io.FileReader;
import java.text.MessageFormat;
import java.text.SimpleDateFormat;
import java.util.*;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * 格式化测试使用的示例类.
 *
 * @author blinkfox on 2017-11-28.
 */
public class FormatTester {

    private static final Logger log = LoggerFactory.getLogger(FormatTester.class);

    /**
     * 格式化.
     */
    private static void formatter() {
        StringBuilder sb = new StringBuilder();
        Formatter formatter = new Formatter(sb, Locale.US);

        // 可重新排序输出.
        formatter.format("%n%4$2s %3$2s %2$2s %1$2s %n", "a", "b", "c", "d"); // -> " d  c  b  a"
        formatter.format(Locale.FRANCE, "e = %+10.4f", Math.E); // -> "e =    +2,7183"
        formatter.format("%nAmount gained or lost since last statement: $ %(,.2f", 6217.58);
        // -> "Amount gained or lost since last statement: $ 6,217.58"

        log.info("打印出格式化后的字符串:{}", formatter);
        formatter.close();
    }

    /**
     * printf打印.
     */
    private static void printf() {
        String filename = "testfile";
        try (FileReader fileReader = new FileReader(filename)) {
            BufferedReader reader = new BufferedReader(fileReader);
            String line;
            int i = 1;
            while ((line = reader.readLine()) != null) {
                System.out.printf("Line %d: %s%n", i++, line);
            }
        } catch (Exception e) {
            System.err.printf("Unable to open file named '%s': %s", filename, e.getMessage());
        }
    }

    /**
     * stringFormat使用.
     */
    private static void stringFormat() {
        // 格式化日期.
        Calendar c = new GregorianCalendar(1995, Calendar.MAY, 23);
        String s = String.format("Duke's Birthday: %1$tm %1$te,%1$tY", c);
        // -> s == "Duke's Birthday: May 23, 1995"
        log.info(s);
    }

    /**
     * 格式化消息.
     */
    private static void messageFormat() {
        String msg = "欢迎光临，当前（{0}）等待的业务受理的顾客有{1}位，请排号办理业务！";
        MessageFormat mf = new MessageFormat(msg);
        String fmsg = mf.format(new Object[]{new Date(), 35});
        log.info(fmsg);
    }

    /**
     * 格式化日期.
     */
    private static void dateFormat() {
        String str = "2010-1-10 17:39:21";
        SimpleDateFormat format = new SimpleDateFormat("yyyyMMddHHmmss");
        try {
            log.info("格式化后的日期:{}", format.format(format.parse(str)));
        } catch (Exception e) {
            log.error("日期格式化出错！", e);
        }
    }

    public static void main(String[] args) {
        formatter();
        stringFormat();
        messageFormat();
        dateFormat();
        printf();
    }

}

/**
* 扫描控制台输入.
*
* @author blinkfox 2017-11-28
*/
public class ScannerTest {

    public static void main(String[] args) {
        Scanner s = new Scanner(System.in);
        System.out.println("请输入字符串：");
        while (true) {
            String line = s.nextLine();
            if (line.equals("exit")) break;
            System.out.println(">>>" + line);
        }
    }

}

Scanner sc = new Scanner(new File("myNumbers"));
while (sc.hasNextLong()) {
    long aLong = sc.nextLong();
}

String input = "1 fish 2 fish red fish blue fish";
Scanner s = new Scanner(input).useDelimiter("\\s*fish\\s*");
System.out.println(s.nextInt());
System.out.println(s.nextInt());
System.out.println(s.next());
System.out.println(s.next());
s.close();

1
2
red
blue