Collections

Collections class
数组 —> Arrays
Collection —> Collections

排序

public class Main {
   public static void main(java.lang.String[] args) {
       String mercury = new String("Mercury");
       String venus = new String("Venus");
       String earth = new String("Earth");
       String mars = new String("Mars");
       String jupiter = new String("Jupiter");
       String saturn = new String("Saturn");
       String uranus = new String("Uranus");
       String neptune = new String("Neptune");
       ArrayList<String> solarSystem = new ArrayList<>(Arrays.asList(mercury, venus, earth, mars,
               jupiter, saturn, uranus, neptune));
       Collections.sort(solarSystem);
       System.out.println(solarSystem);
   }
}

Output:_**[Earth, Jupiter, Mars, Mercury, Neptune, Saturn, Uranus, Venus]**_
_

最大最小

public static void main(java.lang.String[] args) {
   ArrayList<Integer> numbers = new ArrayList<>(Arrays.asList(1,2,3,4,5,6,7));
   System.out.println(Collections.max(numbers));
   System.out.println(Collections.min(numbers));
}

Output:
7
1
_

反转

public class Main {
   public static void main(java.lang.String[] args) {
       String mercury = new String("Mercury");
       String venus = new String("Venus");
       String earth = new String("Earth");
       String mars = new String("Mars");
       String jupiter = new String("Jupiter");
       String saturn = new String("Saturn");
       String uranus = new String("Uranus");
       String neptune = new String("Neptune");
       ArrayList<String> solarSystem = new ArrayList<>(Arrays.asList(mercury, venus, earth, mars,
               jupiter, saturn, uranus, neptune));
       Collections.sort(solarSystem);
       Collections.reverse(solarSystem);
       System.out.println(solarSystem);
   }
}

Output:
[Venus, Uranus, Saturn, Neptune, Mercury, Mars, Jupiter, Earth]
_

乱序

public class Main {
   public static void main(java.lang.String[] args) {
       ArrayList<Integer> bingoDrum = new ArrayList<>(100);
       for (int i = 1; i <= 100; i++) {
           bingoDrum.add(i);// add the numbers 1 to 100 to the drum
       }
       Collections.shuffle(bingoDrum);// Mix it up
       System.out.println ("Your attention, please! Here are the first 10 numbers from the drum!");
       for (int i = 0; i < 10; i++) {
           System.out.println(bingoDrum.get(i));
       }
   }
}

Output:
Your attention, please! Here are the first 10 numbers from the drum!
32
61
4
81
25
8
66
35
42
71
_

交换

public class Main {
   public static void main(java.lang.String[] args) {
       String mercury = new String("Mercury");
       String venus = new String("Venus");
       String earth = new String("Earth");
       String mars = new String("Mars");
       String jupiter = new String("Jupiter");
       String saturn = new String("Saturn");
       String uranus = new String("Uranus");
       String neptune = new String("Neptune");
       ArrayList<String> solarSystem = new ArrayList<>(Arrays.asList(neptune, venus, earth, mars
       , jupiter, saturn, uranus, mercury));// The planets are in the wrong order
       System.out.println(solarSystem);
       Collections.swap(solarSystem, solarSystem.indexOf(mercury), solarSystem.indexOf(neptune));
       System.out.println(solarSystem);
   }
}

Output:
[Neptune, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Mercury]
[Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune]
_

binarySearch

在进行此调用之前，必须根据列表元素的自然顺序对列表进行升序排序（通过 sort(List) 方法）。

也不一定是升序，对列表进行排序的比较器和二分使用的比较器为同一种即可

如果没有对列表进行排序，则结果是不确定的。
如果列表包含多个等于指定对象的元素，则无法保证找到的是哪一个。

如果列表中存在要查找的元素，返回其索引(0 <= index < list.size())
如果不存在，返回(-(index + 1))，其中index为其应该插入的位置，也就是说如果列表为升序排列，index为第一个大于等于被查找元素的索引。