Java 泛型（Generics）

泛型：就是变量类型的参数化

泛型是JDK1.5中的一个最重要的特征。通过引入泛型，我们将获得编译时类型的安全和运行时更小的抛出ClassCastException的可能。

public class ArrayListTest {

	public static void main(String[] args) {

		List list = new ArrayList();

		list.add("Nick");

		list.add(new Integer(20));

		list.add(new Boolean(false));

		String str = (String) list.get(0);

		Integer in = (Integer)list.get(1);

		String b = (String)list.get(2);

	}

}

　　运行后，String b = (String)list.get(2);将抛出异常

Exception in thread "main" java.lang.ClassCastException: java.lang.Boolean cannot be cast to java.lang.String

	at com.example.fanxing.ArrayListTest.main(ArrayListTest.java:16)

定义两个类，如下图

以上两个类结构时一致的，如果在增加一种类型，如String，还需要创建StringDemo类。

可以优化成一个类统一处理：

public class ObjectDemo {

	private Object falg ;

	public Object getFalg() {

		return falg;

	}

	public void Integer(Object falg) {

		this.falg = falg;

	}

}

　　然后使用ObjectDemo

public static void main(String[] args) {

		ObjectDemo obj1 = new ObjectDemo();

		obj1.SetFlag("Nick");

		String falg = (String)obj1.getFalg();

		System.out.println("falg:" + falg);

		ObjectDemo obj2 = new ObjectDemo();

		obj2.SetFlag(new Integer(20));

		Integer falg2 = (Integer)obj2.getFalg();

		System.out.println("falg2:" + falg2);

		String falg3 = (String)obj2.getFalg();

		System.out.println("falg3:" + falg3);

	}

然后String falg3 = (String)obj2.getFalg();异常

java.lang.ClassCastException: java.lang.Integer cannot be cast to java.lang.String

	at com.example.fanxing.ObjectDemo.main(ObjectDemo.java:27)

2、泛型的使用

public class GenericFlag<T> {

	private T  flag;

	public T getFlag() {

		return flag;

	}

	public void setFlag(T flag) {

		this.flag = flag;

	}

	public static void main(String[] args) {

		GenericFlag<Boolean> flag1 = new GenericFlag<Boolean>();

		flag1.setFlag(new Boolean(false));

		GenericFlag<Integer> flag2 = new GenericFlag<Integer>();

		flag2.setFlag(new Integer(20));

		Boolean f1 = flag1.getFlag();

		System.out.println("f1: " + f1);

		Integer f2 = flag2.getFlag();

		System.out.println("f2: " + f2);

	}

}

3、两个泛型的实现方式

public class Generic<T1, T2> {

	private T1 flag1;

	private T2 flag2;

	public T1 getFlag1() {

		return flag1;

	}

	public void setFlag1(T1 flag1) {

		this.flag1 = flag1;

	}

	public T2 getFlag2() {

		return flag2;

	}

	public void setFlag2(T2 flag2) {

		this.flag2 = flag2;

	}

	public static void main(String[] args) {

		Generic<Integer, Boolean> flag = new Generic<Integer, Boolean>();

		flag.setFlag1(new Integer(20));

		flag.setFlag2(new Boolean(false));

		System.out.println(flag.getFlag1());

		System.out.println(flag.getFlag2());

	}

}

4、数组类型的泛型

public class Generic2<T> {

	private T[] flagArray;

	public T[] getFlagArray() {

		return flagArray;

	}

	public void setFlagArray(T[] flagArray) {

		this.flagArray = flagArray;

	}

	public static void main(String[] args) {

		Generic2<String> flag = new Generic2<String>();

		String[] str1 = {"Nick","Tom","Larry"};

		String[] str2 = null;

		flag.setFlagArray(str1);

		str2 = flag.getFlagArray();

		for(int i = 0; i< str2.length ; i++){

			System.out.println(str2[i]);

		}

	}

}

5、模拟ArrayList功能

public class SimpleCollection<T> {

	private T[] objArr;

	private int index = 0;

	public SimpleCollection() {

		objArr = (T[]) new Object[10];

	}

	public SimpleCollection(int capacity) {

		objArr = (T[]) new Object[capacity];

	}

	public void  add(T t) {

		objArr[index++] = t;

	}

	public int getLength() {

		return this.index;

	}

	public T get(int i){

		return objArr[i];

	}

	public static void main(String[] args) {

		SimpleCollection<Integer> s = new SimpleCollection<Integer>();

		for(int i = 0; i < 10; i++){

			s.add(new Integer(i));

		}

		for(int i = 0; i < 10; i++){

			Integer in = s.get(i);

			System.out.println(in);

		}

	}

}

　打印结果

　6、泛型的泛型

/**

 * 泛型的泛型

 *

 */

public class WrapperFlag<T> {

	private GenericFlag3<T>  flag;

	public GenericFlag3<T> getFlag() {

		return flag;

	}

	public void setFlag(GenericFlag3<T> flag) {

		this.flag = flag;

	}

	public static void main(String[] args) {

		GenericFlag3<Integer> flag = new GenericFlag3<Integer>();

		flag.setFlag(100);

		WrapperFlag<Integer> wrapperFlag = new WrapperFlag<Integer>();

		wrapperFlag.setFlag(flag);

		GenericFlag3<Integer> g = wrapperFlag.getFlag();

		System.out.println(g.getFlag());

	}

}

class GenericFlag3<T>{

	private T flag;

	public T getFlag() {

		return flag;

	}

	public void setFlag(T flag) {

		this.flag = flag;

	}

}

6、Set泛型

public class SetTest {

	public static void main(String[] args) {

		Set<String> set = new HashSet<String>();

		set.add("a1");

		set.add("a2");

		set.add("a3");

		for(Iterator<String> iterator = set.iterator(); iterator.hasNext();){

			String value = iterator.next();

			System.out.println(value);

		}

	}

}

7、Set泛型，类型为对象Student

public class SetTest {

	public static void main(String[] args) {

		Set<Student> set2 = new HashSet<Student>();

		set2.add(new Student("tom", 20, "shanghai"));

		set2.add(new Student("Jack", 30, "ShangHai"));

		set2.add(new Student("Nick", 40, "YunNan"));

		for(Iterator<Student> iterator = set2.iterator(); iterator.hasNext();){

			Student student = iterator.next();

			String name = student.getName();

			int age = student.getAge();

			String address = student.getAddress();

			System.out.println(name + "," + age +"," + address);

		}

	}

}

class Student{

	private String name;

	private int age;

	private String address;

	public Student(String name, int age, String address) {

		this.name = name;

		this.age = age;

		this.address = address;

	}

	public String getName() {

		return name;

	}

	public void setName(String name) {

		this.name = name;

	}

	public int getAge() {

		return age;

	}

	public void setAge(int age) {

		this.age = age;

	}

	public String getAddress() {

		return address;

	}

	public void setAddress(String address) {

		this.address = address;

	}

	@Override

	public int hashCode() {

		final int prime = 31;

		int result = 1;

		result = prime * result + ((address == null) ? 0 : address.hashCode());

		result = prime * result + age;

		result = prime * result + ((name == null) ? 0 : name.hashCode());

		return result;

	}

	@Override

	public boolean equals(Object obj) {

		if (this == obj)

			return true;

		if (obj == null)

			return false;

		if (getClass() != obj.getClass())

			return false;

		Student other = (Student) obj;

		if (address == null) {

			if (other.address != null)

				return false;

		} else if (!address.equals(other.address))

			return false;

		if (age != other.age)

			return false;

		if (name == null) {

			if (other.name != null)

				return false;

		} else if (!name.equals(other.name))

			return false;

		return true;

	}

}

8、Map泛型

public class MapTest {

	public static void main(String[] args) {

		Map<String, String> map  = new HashMap<String, String>();

		map.put("a", "aa");

		map.put("b", "bb");

		map.put("c", "cc");

		map.put("d", "dd");

		//方式一

		Set<String> set = map.keySet();

		for(Iterator<String> iter = set.iterator(); iter.hasNext();){

			String key = iter.next();

			String value = map.get(key);

			System.out.println("key:" + key + " value:" + value);

		}

		System.out.println("--------------------");

		//方式二

		Set<Map.Entry<String, String>> entriesSet = map.entrySet();

		for(Iterator<Map.Entry<String, String>> iter = entriesSet.iterator(); iter.hasNext();){

			Map.Entry<String, String> entry = iter.next();

			String key = entry.getKey();

			String value = entry.getValue();

			System.out.println("key:" + key + " value:" + value);	

		}

	}

}

巴特西

Java 泛型（Generics）

最新文章

热门文章

巴特西

Java 泛型 （Generics）

最新文章

热门文章

Java 泛型（Generics）