“泛型”总结_JAVA_编程开发_程序员俱乐部

泛型是JDK1.5中一个最重要的特征。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地抛出ClassCastException的可能。
在JDK1.5中，你可以声明一个集合将接收/返回的对象的类型。

泛型特点：只要编译的时候没有问题，执行的时候肯定没有问题。

泛型之前：
类别定义时的逻辑完全一样，只是里面成员变量的类型不同。
如果需要多个相似的类，需要定义多个文件，不同的只是变量的类型，而逻辑是完全一样的。



以后使用集合的时候必须要使用泛型（可以避免很多强制类型转换）
迭代器迭代过程中迭代器也要加上泛型

以下是各种集合类在遍历的时候使用泛型的标准写法，以后把这个作为标准都这么写：

class="java" name="code">package com.shengshiyuan4;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

public class ArrayListTest {
	public static void main(String[] args) {
		List<String> list = new ArrayList<String>();
		list.add("a");
		list.add("b");
		list.add("c");
		list.add("d");
		for (int i = 0; i < list.size(); i++) {
			String value = list.get(i);
			System.out.println(value);
		}

		for (Iterator<String> iter = list.iterator(); iter.hasNext();) {
			String value = iter.next();
			System.out.println(value);
		}
	}
}

package com.shengshiyuan4;

import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;

public class SetTest {
	public static void main(String[] args) {
		Set<String> set = new HashSet<String>();
		set.add("aa");
		set.add("bb");
		set.add("cc");

		for (Iterator<String> iter = set.iterator(); iter.hasNext();) {
			String value = iter.next();
			System.out.println(value);
		}

		System.out.println("--------------------------------");
		Set<People> set2 = new HashSet<People>();
		set2.add(new People("zhangsan", 20, "beijing"));
		set2.add(new People("lishi", 30, "shanghai"));
		set2.add(new People("wangwu", 40, "guangzhou"));

		for (Iterator<People> iter = set2.iterator(); iter.hasNext();) {
			People people = iter.next();
			String name = people.getName();
			String address = people.getAddress();
			int age = people.getAge().intValue();
			System.out.println(name + "," + age + "," + address);
		}
	}
}

class People {
	private String name;
	private Integer age;
	private String address;

	public People(String name, Integer age, String address) {
		this.name = name;
		this.age = age;
		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 == null) ? 0 : age.hashCode());
		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;
		final People other = (People) obj;
		if (address == null) {
			if (other.address != null)
				return false;
		} else if (!address.equals(other.address))
			return false;
		if (age == null) {
			if (other.age != null)
				return false;
		} else if (!age.equals(other.age))
			return false;
		if (name == null) {
			if (other.name != null)
				return false;
		} else if (!name.equals(other.name))
			return false;
		return true;
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public Integer getAge() {
		return age;
	}

	public void setAge(Integer age) {
		this.age = age;
	}

	public String getAddress() {
		return address;
	}

	public void setAddress(String address) {
		this.address = address;
	}

}

package com.shengshiyuan4;

import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;

public class MapTest {
	public static void main(String[] args) {
		Map<String, String> map = new HashMap<String, String>();
		map.put("1", "aa");
		map.put("2", "bb");
		map.put("3", "cc");

		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 + ";" + value);
		}

		Set<Map.Entry<String, String>> set2 = map.entrySet();
		for (Iterator<Map.Entry<String, String>> iter = set2.iterator(); iter
				.hasNext();) {
			Map.Entry<String, String> entry = iter.next();
			String key = entry.getKey();
			String value = entry.getValue();
			System.out.println(key + ";" + value);
		}
	}
}