1
public class MyLinkedList {
2
   private int size;
3
   private Node first;
4
private Node last;
5
//向链表的尾部添加节点
6
public boolean add(Object obj){
7
    Node node = new Node(obj);
8
    //链表中一个节点没有的情况
9
    if(first==null){
10
        first = last = node;
11
    }else {
12
        //链表中有节点的情况
13
        node.prev = last;
14
        //为了不丢失原尾节点的引用，最后设置last的引用
15
        last.next = node;
16
        last = node;
17
    }
18
    size++;
19
    return true;
20
}
21
public void add(int index,Object obj){
22
    checkIndex(index,size+1);
23
    Node newNode = new Node(obj);
24
    //链表中一个节点没有的情况
25
    if(first==null){
26
        first = last = newNode;
27
    }else{
28
        if(index==size){
29
            add(obj);
30
        }else {
31
            //找到插入位置的节点
32
            Node node = getNode(index);
33
            newNode.prev = node.prev;
34
            newNode.next = node;
35
            node.prev.next = newNode;
36
            node.prev = newNode;
37
        }
38
    }
39
    size++;
40
}
41
public void clear(){
42
    first = last = null;
43
    size = 0;
44
}
45
public boolean contains(Object obj){
46
    return indexOf(obj)!=-1;
47
}
48
public Object get(int index){
49
    //验证index是否超出范围
50
    checkIndex(index,size);
51
    return getNode(index).data;
52
}
53
public int indexOf(Object obj){
54
    if (first == null) return -1;
55
    Node node = first;
56
    for (int i = 0; i < size; i++) {
57
        if(obj==null){
58
            if(node==null) {
59
                return i;
60
            }
61
        }else{
62
            if(obj.equals(node.data)){
63
                return i;
64
            }
65
        }
66
        node = node.next;
67
    }
68
    return -1;
69
}
70
public Object remove(int index){
71
    checkIndex(index,size);
72
    Object o = null;
73
    //只有一个节点
74
    if(size==1){
75
        o = first;
76
        first = last = null;
77
    }else if(index == 0){
78
        //多个节点，删除的是头结点
79
        o = first;
80
        first = first.next;
81
        first.prev.next = null;
82
        first.prev = null;
83
    }else if(index == size-1) {
84
        //多个节点，删除的是尾节点
85
        o = last;
86
        last = last.prev;
87
        last.next.prev = null;
88
        last.next = null;
89
    }else {
90
        //多个节点，删除的不是头和尾节点
91
        Node node = getNode(index);
92
        o = node;
93
        node.prev.next = node.next;
94
        node.next.prev = node.prev;
95
        node.prev = null;
96
        node.next = null;
97
    }
98
    size--;
99
    return o;
100
}
101
public boolean remove(Object obj){
102
    return true;
103
}
104
public Object set(int index,Object obj){
105
    checkIndex(index,size);
106
    Node node = getNode(index);
107
    Object o = node.data;
108
    node.data = obj;
109
    return o;
110
}
111
public int size(){
112
    return size;
113
}
114
//封装一个根据索引找节点的方法
115
private Node getNode(int index){
116
    //index和size/2 比较，从前遍历还是从后遍历
117
    if(index <= size>>1){
118
        Node node = first;
119
        //从前向后遍历
120
        for (int i = 0; i < index; i++) {
121
            node = node.next;
122
        }
123
        return node;
124
    }else {
125
        Node node = last;
126
        //从后向前遍历
127
        for (int i = size-1; i > index ; i--) {
128
            node = node.prev;
129
        }
130
        return node;
131
    }
132
}
133
private void checkIndex(int index,int size){
134
    if(index<0 || index >= size){
135
        throw new IndexOutOfBoundsException();
136
    }
137
}
138
private class Node{
139
    private Object data;
140
    private Node prev;
141
    private Node next;
142
    public Node(Object data){
143
        this.data = data;
144
    }
145
    public Node(Object data, Node prev, Node next) {
146
        this.data = data;
147
        this.prev = prev;
148
        this.next = next;
149
    }
150
}
151
public static void main(String[] args) {
152
    MyLinkedList list = new MyLinkedList();
153
    list.add("a");
154
    list.add("b");
155
    list.add("c");
156
    list.add("d");
157
    list.add("e");
158
    list.add(2,"C");
159
    for (int i = 0; i < list.size; i++) {
160
        System.out.println(list.get(i));
161
        }
162
    }
163
}

1
public class Person implements Comparable<Person>{
2
    String name;
3
    int age;
4
    double height;
5
    int score;
6
    public Person(String name, int age, double height,int score) {
7
        this.name = name;
8
        this.age = age;
9
        this.height = height;
10
        this.score = score;
11
    }
12
    @Override
13
    public int compareTo(Person o) {
14
        //比较的结果是 返回三种值  0 ，大于0，小于0
15
        //如果两个人的年龄相同，则再按身高比较
16
        if(this.age==o.age){
17
            if(this.height>o.height){
18
                return 1;
19
            }else{
20
                return -1;
21
            }
22
        }
23
        return this.age - o.age;
24
    }
25
    public static void main(String[] args) {
26
        List<Person> list = new ArrayList<>();
27
        Collections.addAll(list,
28
                new Person("二哥",20,1.75,70),
29
                new Person("三哥",20,1.72,90),
30
                new Person("大哥",22,1.71,55));
31
        //Collections.sort(list);
32
        //Collections.sort(list,new PersonScoreComparator());
33
        Collections.sort(list, new Comparator<Person>() {
34
            @Override
35
            public int compare(Person o1, Person o2) {
36
                return o1.score - o2.score;
37
            }
38
        });
39
        for (int i = 0; i < list.size(); i++) {
40
            System.out.println(list.get(i).name);
41
        }
42
        List<String> list2 = new ArrayList<>();
43
        Collections.addAll(list2,"cac","bcd","abc");
44
        Collections.sort(list2);
45
        System.out.println(list2);
46
    }
47
}

1
 List<String> list = new ArrayList<>();
2
 Collections.addAll(list,"a","b","c");
3
 for (String str:list){
4
    list.remove("a");
5
    System.out.println(str);
6
 }

1
HashSet<String> set = new HashSet<>();
2
Collections.addAll(set,"a","b","c");
3
for (String str:set){
4
    System.out.println(str);
5
}
6
 HashMap<String,String> map = new HashMap<>();
7
 map.put("101","a");
8
 map.put("102","b");
9
 map.put("103","c");
10
 Set<Map.Entry<String,String>> set = map.entrySet();
11
 for(Map.Entry<String,String> entry:set){
12
    System.out.println(entry.getKey()+","+entry.getValue());
13
 }
14
HashMap<String,String> map = new HashMap<>();
15
map.put("101","a");
16
map.put("102","b");
17
map.put("103","c");
18
Set<String> set = map.keySet();
19
for (String key :set) {
20
    System.out.println(key);
21
}

1
 /*String[] strs = new String[]{"a","b","c"};
2
 for(String str:strs){
3
    System.out.println(str);
4
 }*/
5
 String[][] arr = new String[][]{{"a","b"},{"c","d"}};
6
 for(String[] strs:arr){
7
    for(String str:strs){
8
        System.out.println(str);
9
    }
10
 }