贴一些演示简单API的代码

有部分使用不正确，不要模仿：

/** * enum */ package com; /** * @author Administrator * */ public class EnumTest { enum Week { Mon, Tue, Wed, Thu, Fri, Sat, Sun } /** * @param args */ public static void main(String[] args) { System.out.println(Week.valueOf("Mon")); // System.out.println(Week.Mon); System.out.println(Week.Sun); Week[] w = Week.values(); for (Week we : w) { System.out.println(we); } switch (Week.Sun) { case Mon: System.out.println("1"); break; default: System.out.println("default"); } System.out.println(Week.Mon.compareTo(Week.Fri)); System.out.println(Coffee.small); System.out.println(Coffee.small.getSize()); Coffee[] coffee = Coffee.values(); for(Coffee c: coffee) { System.out.println(c); System.out.println(c.getSize()); } System.out.println(Week.valueOf("Mon1")); } } enum Coffee { small(8), middle(10), large(12); private int size; Coffee(int size) { this.size = size; } public int getSize() { return size; } }

Exception in thread "main" java.lang.IllegalArgumentException: No enum const class com.EnumTest$Week.Mon1 at java.lang.Enum.valueOf(Enum.java:196) at com.EnumTest$Week.valueOf(EnumTest.java:1) at com.EnumTest.main(EnumTest.java:48) Mon Mon Sun Mon Tue Wed Thu Fri Sat Sun default -4 small 8 small 8 middle 10 large 12

/** * */ package com; /** * @author Administrator * */ public class ForTest { public static void main(String[] args) { for (int i = 0, j = 10; i < 10;) { System.out.println(i + j); i++; } } }

10 11 12

/** * */ package com; import java.util.ArrayList; import java.util.List; /** * @author Administrator * */ public class TestWildcards { public static void main(String[] args) { List<Integer> myList = new ArrayList<Integer>(); Bar bar = new Bar(); bar.doInsert(myList); } } class Bar { void doInsert(List<? extends Object> list) { list.contains(new Dog()); // 说不清楚具体是什么 可添加多种对象而造成危险 比如 Cat Dog等。 list.add(new Object); // compile error } } class Bar2 { void doInsert(List<? super String> list) { list.contains(new Dog()); // string is a ? 合理 list.add("test"); } }

import java.util.Comparator; import java.util.PriorityQueue; /** * */ /** * @author Administrator * */ public class PriorityQueueTest { static class PQsort implements Comparator<Integer> { // inverse sort public int compare(Integer one, Integer two) { return two - one; // unboxing } } public static void main(String[] args) { int[] ia = { 1, 5, 3, 7, 6, 9, 8 }; // unordered data PriorityQueue<Integer> pq1 = new PriorityQueue<Integer>(); // use // natural // order for (int x : ia) // load queue pq1.offer(x); for (int x : ia) // review queue System.out.print(pq1.poll() + " "); System.out.println(""); PQsort pqs = new PQsort(); // get a Comparator PriorityQueue<Integer> pq2 = new PriorityQueue<Integer>(10, pqs); // use // Comparator for (int x : ia) // load queue pq2.offer(x); System.out.println("size " + pq2.size()); System.out.println("peek " + pq2.peek()); System.out.println("size " + pq2.size()); System.out.println("poll " + pq2.poll()); System.out.println("size " + pq2.size()); for (int x : ia) // review queue System.out.print(pq2.poll() + " "); } }

1 3 5 6 7 8 9 size 7 peek 9 size 7 poll 9 size 6 8 7 6 5 3 1 null

/** * */ package com; import java.util.ArrayList; import java.util.Collections; import java.util.Comparator; import java.util.List; /** * @author Administrator * */ public class CollectionsTest { /** * @param args */ public static void main(String[] args) { List list = new ArrayList(); list.add("a"); list.add("b"); list.add("c"); list.add("a23"); Collections.sort(list); int i = Collections.binarySearch(list, "a23"); System.out.println(list); PQsort pq = new PQsort(); Collections.sort(list,pq); int j = Collections.binarySearch(list, "a23"); System.out.println(i); System.out.println(j); int m = Collections.binarySearch(list, "a23", pq); System.out.println(m); System.out.println(list); } } class PQsort implements Comparator<String> { // inverse sort public int compare(String one, String two) { return two.compareTo(one); // unboxing //return one.compareTo(two); // unboxing } }

[a, a23, b, c] 1 -1 2 [c, b, a23, a]

/** * */ package file; import java.io.BufferedReader; import java.io.File; import java.io.FileInputStream; import java.io.FileNotFoundException; import java.io.FileReader; import java.io.FileWriter; import java.io.IOException; import java.io.Serializable; /** * @author Administrator * */ public class FileTest implements Serializable { public static void main(String[] args) { String filePath = "d://test"; File file = new File(filePath); file.mkdir(); File fileName = new File("d://test//t.dat"); try { fileName.createNewFile(); } catch (IOException e)