java集合框架

容器API

Collection接口

equals & hashCode

注意：重寫equals方法必須重寫hashCode方法，如果A.equals(B)，那麼A和B的hashCode碼相等。

//姓名
public class Name /*implements Comparable*/{
    private String firstName;
    private String lastName;

    public Name(String firstName, String lastName) {
        this.firstName = firstName;
        this.lastName = lastName;
    }

    public String getFirstName() {
        return firstName;
    }

    public String getLastName() {
        return lastName;
    }

    @Override
    public String toString() {
        return firstName + " " + lastName;
    }

    @Override
    public boolean equals(Object obj) {
        if(obj instanceof Name) {
            Name name = (Name) obj;
            return (firstName.equals(name.firstName)) 
            && (lastName.equals(name.lastName));
        }
        return super.equals(obj);
    }

    @Override
    public int hashCode() {
        return firstName.hashCode();  //String類實現了hashCode()方法
    }

    /*
    @Override
    public int compareTo(Object o) {
        Name name = (Name) o;
        int last = lastName.compareTo(name.lastName);
        return (last != 0 ? last : firstName.compareTo(name.firstName));
    }*/
}

//容器基礎
public class BaseContainer {
    public static void main(String[] args) {
        Collection c = new HashSet();
        c.add("hello");
        c.add(new Name("Li", "Jun"));
        c.add(new Integer(100));
        c.remove("hello");
        c.remove(new Integer(100));
        System.out.println(c.remove(new Name("Li", "Jun")));//false
        System.out.println(c);  //[Li Jun]
    }
}

Iterator接口

//迭代器
public class IteratorTest {
    public static void main(String[] args) {
        Collection c = new HashSet();
        c.add(new Name("Li", "Jun"));
        c.add(new Name("Hao", "yun"));
        c.add(new Name("Ai", "Ya"));
        Iterator i = c.iterator();
        while(i.hasNext()) {
            //next()的返回值爲Object類型，需轉換爲相應類型
            Name name = (Name) i.next();
            System.out.print(name.getFirstName() + " ");  //Hao Li Ai
        }

        for(Iterator j = c.iterator(); j.hasNext();) {
            Name n = (Name)j.next();
            if(n.getFirstName().length() < 3) {
                j.remove();
            }
        }
        System.out.println(c);    //[Hao yun]
    }
}

Set接口

//Set接口
public class SetTest {
    public static void main(String[] args) {
        Set s = new HashSet();
        s.add("hello");
        s.add(new Name("Li", "Jun"));
        s.add(new Integer(100));
        s.add("hello");  //重複元素不會加入Set
        s.add(new Name("Li", "Jun"));
        System.out.println(s);   //[hello, 100, Li Jun]
    }
}

//方法測試
public class MethodInSet {
    public static void main(String[] args) {
        Set s1 = new HashSet();
        Set s2 = new HashSet();
        s1.add("a"); s1.add("b"); s1.add("c"); 
        s2.add("d"); s2.add("a"); s2.add("b");
        //Set和List容器類都具有Constructor(Collection c)
        //構造方法用以初始化容器類
        Set sn = new HashSet(s1);
        sn.retainAll(s2); //求交集
        Set su = new HashSet(s1);
        su.addAll(s2);    //將集合s2中的所有元素加入s1中
        System.out.println(sn);  //[b, a]
        System.out.println(su);  //[d, b, c, a]
    }
}

List接口

//List接口中的方法
public class MethodInList {
    public static void main(String[] args) {
        List list = new LinkedList();
        for(int i = 0; i <= 4; i++) {
            list.add("G" + i);
        }
        System.out.println(list);  //[G0, G1, G2, G3, G4]
        list.add(1, "G100");
        System.out.println(list);  //[G0, G100, G1, G2, G3, G4]
        list.set(1, "G20");
        System.out.println(list);  //[G0, G20, G1, G2, G3, G4]
        System.out.print(list.get(1) + " ");
        System.out.println(list.indexOf("G1"));  //G20 2
        list.remove(1);
        System.out.println(list);  //[G0, G1, G2, G3, G4]
    }
}

List常用算法

//List中的常用算法
public class AlgorithmInList {
    public static void main(String[] args) {
        List list = new LinkedList();
        for(int i = 0; i <= 5; i++) {
            list.add("a" + i);
        }
        System.out.println(list);   //[a0, a1, a2, a3, a4, a5]
        Collections.shuffle(list);  //隨機排列
        System.out.println(list);   //[a0, a2, a5, a1, a4, a3]
        Collections.reverse(list);  //逆序
        System.out.println(list);   //[a3, a4, a1, a5, a2, a0]
        Collections.sort(list);     //排序
        System.out.println(list);   //[a0, a1, a2, a3, a4, a5]
        System.out.println(Collections.binarySearch(list, "a3"));  //二分查找
    }
}

Comparable接口

//Comparable接口
public class ComparableTest {
    public static void main(String[] args) {
        List list = new LinkedList();
        list.add(new Name("Karl", "M"));
        list.add(new Name("Yun", "Hao"));
        list.add(new Name("John", "O"));
        list.add(new Name("Tom", "M"));
        System.out.println(list);  //[Karl M, Yun Hao, John O, Tom M]
        Collections.sort(list);    //會調用compareTo方法
        System.out.println(list);  //[Yun Hao, Karl M, Tom M, John O]
    }
}

Map接口

//Map接口中的方法
public class MethodInMap {
    public static void main(String[] args) {
        Map<String, Integer> m1 = new HashMap<String, Integer>();
        Map m2 = new TreeMap();
        /*m1.put("one", new Integer(1));
        m1.put("two", new Integer(2));
        m1.put("three", new Integer(3));*/
        m1.put("one", 1);
        m1.put("two", 2);
        m1.put("three", 3);
        /*m2.put("A", new Integer(1));
        m2.put("B", new Integer(2));*/
        m2.put("A", 1);
        m2.put("B", 2);
        System.out.println(m1.size()); //3
        System.out.println(m1.containsKey("one"));//true
        System.out.println(m2.containsValue(1)); //true
        if(m1.containsKey("two")) {
            //int i = ((Integer) m1.get("two")).intValue();
            int i = m1.get("two");
            System.out.println(i);   //2
        }
        Map m3 = new HashMap(m1);
        m3.putAll(m2);
        System.out.println(m3);    //{two=2, A=1, B=2, one=1, three=3}
    }
}

泛型

//泛型
public class Template {
    public static void main(String[] args) {
        List<String> c = new ArrayList<String>();
        c.add("aaa");
        c.add("bbb");
        c.add("ccc");
        for(int i = 0; i < c.size(); i++) {
            String s = c.get(i);
            System.out.println(s);
        }

        Collection<String> c2 = new HashSet<String>();
        c2.add("aaa"); c2.add("bbb"); c2.add("ccc");
        for(Iterator<String> it = c2.iterator(); it.hasNext();) {
            String s = it.next();
            System.out.println(s);
        }
    }
}
//泛型類
class MyName implements Comparable<MyName> {
    int age;
    public int compareTo(MyName mn) {
        if(this.age > mn.age) return 1;
        else if(this.age < mn.age) return -1;
        else return 0;
    }
}