集合框架

迭代器(Iterable)

实现Iterable接口的类都可以用for-each来遍历。

Iterator iterator = list.iterator();// 迭代器

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ArrayList底层用数组储存，遍历元素和随机访问元素效率高，添加元素删除元素效率低。
例：

import java.util.ArrayList;import java.util.List;import javax.swing.SpringLayout.Constraints;public class TestModify {    public static void main(String[] args) {        List list = new ArrayList();        list.add("aaa");        list.add("bbb");        list.add("ccc");        print(list);        System.out.println("=============");        /**         * 替换指定位置的元素         */        // list.set(1, "2");        // print(list);        /**         * 删除所有元素         */        // list.clear();        // print(list);        /**         * 查找集合中是否存在指定元素         */        boolean contains = list.contains("aaa");        System.out.println(contains);    }    private static void print(List list) {        // TODO Auto-generated method stub        for (int i = 0; i < list.size(); i++) {            System.out.println(list.get(i));        }        if (list.size() == 0) {            System.out.println("meile");        }    }}

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删除元素，例：

import java.util.ArrayList;import java.util.List;import javax.swing.SpringLayout.Constraints;public class TestModify {    public static void main(String[] args) {        List list = new ArrayList();        list.add("aaa");        list.add("bbb");        list.add("ccc");        print(list);        System.out.println("=============");        /**         * 替换指定位置的元素         */        // list.set(1, "2");        // print(list);        /**         * 删除所有元素         */        // list.clear();        // print(list);        /**         * 查找集合中是否存在指定元素         */        boolean contains = list.contains("aaa");        System.out.println(contains);    }    private static void print(List list) {        // TODO Auto-generated method stub        for (int i = 0; i < list.size(); i++) {            System.out.println(list.get(i));        }        if (list.size() == 0) {            System.out.println("meile");        }    }}

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LinkedList底层用链表储存，插入和删除元素效率高，遍历和随机访问效率低。
例：

import java.util.Iterator;import java.util.LinkedList;import java.util.List;public class TestLinked {    public static void main(String[] args) {        List list = new LinkedList<>();        list.add("aaa");        list.add("bbb");        list.add("ccc");        print(list);        System.out.println("================");        List temp = new LinkedList<>();        temp.add("ddd");        temp.add("aaa");        print(temp);        System.out.println("================");        /**         * 删除两个集合相同的地方         */        list.removeAll(temp);        print(list);    }    /**     * 加强for遍历     */    private static void print(List list) {        // TODO Auto-generated method stub        for (Object o : list) {            System.out.println(o);        }    }}

List添加顺序和访问顺序是一致的，能添加重复元素。

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HashSet底层用数组+链表，添加速度快，删除速度快，查询速度快，无序。
例：

import java.util.HashSet;import java.util.Set;public class TestHash {    public static void main(String[] args) {        Set set = new HashSet();        set.add("aaa");        /**         * 添加是否成功         */        // boolean is = set.add("aaa");        // System.out.println(is);        set.add("bbb");        set.add("ccc");        print(set);        /**         * 查看集合中是否存在元素         */        boolean contains = set.contains("ccc");        System.out.println(contains);    }    private static void print(Set set) {        // TODO Auto-generated method stub        for (Object o : set) {            System.out.println(o);        }    }}

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重写Hashcode方法和equals方法
去重
例：

public class Student {    private String name;    public Student(String name) {        this.name=name;    }    @Override    public String toString() {        return "姓名:"+name;    }    @Override    public int hashCode() {        // 相同的字符串肯定具有相同的hashcode        return name.hashCode();    }    @Override    public boolean equals(Object obj) {        return true;    }}

import java.util.HashSet;import java.util.Set;public class TestStudent {    public static void main(String[] args) {        Set set = new HashSet<>();        set.add(new Student("张三"));        set.add(new Student("李四"));        set.add(new Student("王五"));        set.add(new Student("李四"));        set.add(new Student("李四"));        set.add(new Student("李四"));        print(set);    }    private static void print(Set set) {        // TODO Auto-generated method stub        for(Object o:set){            System.out.println(o);        }    }}

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TreeSet 底层采用二叉树粗存结构，有序，查询比List快，没有HashSet快；需要实现Comparable。

public class Student implements Comparable<Student> {    private String name;    private int age;    private boolean sex;    public Student(String name, int age, boolean sex) {        super();        this.name = name;        this.age = age;        this.sex = sex;    }    public String getName() {        return name;    }    public int getAge() {        return age;    }    public boolean isSex() {        return sex;    }    @Override    public String toString() {        // TODO Auto-generated method stub        return "姓名" + name + "年龄" + age + "性别" + sex;    }    @Override    public int compareTo(Student o) {        // TODO Auto-generated method stub        return 0;    }}

TreeSet使用CompareTo去重，还能排序。
本例中写的排序方式是：按年龄排序、年龄相同按姓名排、姓名相同按性别排。

import java.util.Comparator;import java.util.Set;import java.util.TreeSet;public class Tree {    public static void main(String[] args) {        Set set = new TreeSet<>(new Comparator<Student>() {            @Override            public int compare(Student o1, Student o2) {                // TODO Auto-generated method stub                int c = o1.getAge() - o2.getAge();                if (c != 0) {                    return c;                }                c = o1.getName().compareTo(o2.getName());                if (c != 0) {                    return c;                }                return new Boolean(o1.isSex()).compareTo(o2.isSex());            }        });        set.add(new Student("张三", 10, true));        set.add(new Student("李四", 10, false));        set.add(new Student("张三", 11, true));        set.add(new Student("张三", 10, false));        set.add(new Student("李四", 10, false));        print(set);    }    private static void print(Set set) {        // TODO Auto-generated method stub        for (Object o : set) {            System.out.println(o);        }    }}

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MAP（映射）

返回一对键值对，通过键获得值，键不允许重复，重复就覆盖，但是值允许重复
HashMap允许使用null键null值
TreeMap Key必须实现Comparable
例：

import java.util.HashMap;import java.util.Map;import java.util.Set;public class TestMap {    public static void main(String[] args) {         Map map = new HashMap<>();        map.put("a", "abc");        map.put("b", "bcd");        map.put("c", "cde");        print(map);    }    private static void print(Map map) {        // TODO Auto-generated method stub        Set keySet = map.keySet();        for(Object key:keySet){            System.out.println(key+"--->"+map.get(key));        }    }}

public class Student {    private String name;    private int age;    public Student(String name, int age) {        super();        this.name = name;        this.age = age;    }    @Override    public String toString() {        // TODO Auto-generated method stub        return "姓名"+name+"，年龄"+age;    }}

import java.util.HashMap;import java.util.Map;import java.util.Set;public class TestMap {    public static void main(String[] args) {        Map map = new HashMap<>();        map.put("f", "fgh");        map.put("a", "abc");        map.put("v", "vbn");        map.put("b", "bcd");        map.put("z", "zxc");        map.put("c", "cde");        print(map);    }    private static void print(Map map) {        // TODO Auto-generated method stub        Set keySet = map.keySet();        for (Object key : keySet) {            System.out.println(key + "--->" + map.get(key));        }    }}

import java.util.HashMap;import java.util.Map;import java.util.Set;public class TestMap1 {    public static void main(String[] args) {        Map map = new HashMap<>();        map.put(new Student("张三", 1), new Student("张三", 10));        map.put(new Student("李四", 1), new Student("李四", 9));        map.put(new Student("王五", 1), new Student("zhangsan", 2));        print(map);    }    private static void print(Map map) {        // TODO Auto-generated method stub        Set keySet = map.keySet();        for(Object key:keySet){            System.out.println(key+"==="+map.get(key));        }    }}

import java.util.Map;import java.util.Set;import java.util.TreeMap;public class TestTreeMap {    public static void main(String[] args) {        Map map = new TreeMap<>();        map.put(new Student("张三", 1), new Student("张三", 10));        map.put(new Student("李四", 1), new Student("李四", 9));        map.put(new Student("王五", 1), new Student("zhangsan", 2));        print(map);    }    private static void print(Map map) {        // TODO Auto-generated method stub        Set keySet = map.keySet();        for (Object key : keySet) {            System.out.println(key + "====" + map.get(key));        }    }}

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泛型

解决数据类型操作不同意产生的异常。

public class Student {    private String name;    private int age;    public Student(String name, int age) {        super();        this.name = name;        this.age = age;    }    @Override    public String toString() {        // TODO Auto-generated method stub        return "姓名"+name+"年龄"+age;    }}

import java.util.ArrayList;import java.util.List;public class TestGenray {    public static void main(String[] args) {        List<String> list= new ArrayList<>();        list.add("aaa");        list.add("bbb");        print(list);        List<Student> list1 = new ArrayList<>();        list1.add(new Student("张三", 10));        list1.add(new Student("李四", 20));        print1(list1);    }    private static void print1(List<Student> list1) {        // TODO Auto-generated method stub        for(Student s:list1){            System.out.println(s);        }    }    private static void print(List<String> list) {        // TODO Auto-generated method stub        for(String s:list){            System.out.println(s);        }    }}

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