JDK1.5新特性

JDK 5.0 的一个重要主题就是通过新增一些特性来简化开发，这些特性包括：

1.静态导入

2.自动装箱/拆箱

3.for-each循环

4.可变参数

5.枚举

6.泛型

7.注解

使用这些特性有助于编写更加清晰，精悍，安全的代码。

静态导入:

import static java.lang.Math.*;
import static java.lang.System.out;
//import static java.math.*;
public class StaticAttr {
    public static void main(String[] args) {
        out.println("xx");
        out.println(PI);
        out.println(abs(-1));
        out.println(pow(1.5,2.2));
    }
}

自动装箱/拆箱

public class Zy2 {
    public static void main(String[] args) {
        Integer a=300;
        Integer b=300;
        System.out.println(a.equals(b));
        System.out.println(a==b);
        System.out.println("-------------");
        Integer d=127;
        Integer c=127;
        System.out.println(d.equals(c));
        System.out.println(d==c);
        System.out.println("-------------");
        Integer it=Integer.valueOf(103);
        Integer it2=Integer.valueOf(103);
        System.out.println(it.equals(it2));
        System.out.println(it==it2);
    }
}

for-each循环

public class Foreach {
    public static void main(String[] args) {
        ArrayList list=new ArrayList();
        list.add(1);
        list.add(2);
        list.add(3);
        for (int i = 0; i < list.size(); i++) {
            System.out.println(list.get(i));
        }
        Set<String> set=new HashSet<>();
        set.add("a");
        set.add("b");
        set.add("c");

        for (String s: set) {
            System.out.println(s);
        }
    }

}

可变参数

public class Foreach {
    public static void main(String[] args) {
        ArrayList list=new ArrayList();
        list.add(1);
        list.add(2);
        list.add(3);
        for (int i = 0; i < list.size(); i++) {
            System.out.println(list.get(i));
        }
        Set<String> set=new HashSet<>();
        set.add("a");
        set.add("b");
        set.add("c");

        for (String s: set) {
            System.out.println(s);
        }
    }

}

枚举

public enum  Season implements IPrinter{
    春天{
        @Override
        public void show(){
            System.out.println("春天");
        }
        public void print(){
            //TO DO
        }
    },
    夏天{
        @Override
        public void show(){
            System.out.println("夏天");
        }
        public void print(){
            //TO DO
        }
    },
    秋天{
        @Override
        public void show(){
            System.out.println("秋天");
        }
        @Override
        public void print(){
            //TO DO
        }
    },
    冬天{
        @Override
        public void show(){
            System.out.println("冬天");
        }
        @Override
        public void print(){
            //TO DO
        }
    }

    ;


    public abstract void show();

}

public interface  IPrinter {
    void print();
}

import java.util.Scanner;

public class Zy5 {
    public static void main(String[] args) {
        Season Season1= Season.春天;
        Season Season2= Season.冬天;
        Season Season3= Season.夏天;

        Season[] seasons = Season.values();
        for (Season xx:seasons) {
            System.out.println(xx.name());
            System.out.println(xx.ordinal());

        }
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入一个季节:");
        String temp = scanner.next();
        //将string--->枚举类型
        Season se=Season.valueOf(temp);
        se.show();

        System.out.println("请选择一个季节编号:");
        int no = scanner.nextInt();
        //将数字-->枚举类型
        Season se1 = Season.values()[no];
        se1.show();

    }

}

技术总结:

1.1 JDK5.0增加的静态导入语法用于导入指定类的某个静态属性值(方法)或全部静态属性值(方法)

静态导入语句使用 import static 语句

导入指定类的单个静态属性:

import static java.lang.System.out

导入指定类全部静态属性

import static java.lang.Math.*