JDK新特性

JDK新特性
(1)JDK5
装箱和拆箱
泛型
增强for

静态导入

public class Direction {
	// 创建几个实例
	public static final Direction FRONT = new Direction();
	public static final Direction BEHIND = new Direction();
	public static final Direction LEFT = new Direction();
	public static final Direction RIGHT = new Direction();

	// 构造私有，别人就不能无限的创建了
	private Direction() {
	}
}

public class Direction2 {
	// 创建几个实例
	public static final Direction2 FRONT = new Direction2("前");
	public static final Direction2 BEHIND = new Direction2("后");
	public static final Direction2 LEFT = new Direction2("左");
	public static final Direction2 RIGHT = new Direction2("右");

	// 构造私有，别人就不能无限的创建了
	// private Direction2() {
	// }

	// 加入成员变量,并去掉无参构造
	private String name;

	private Direction2(String name) {
		this.name = name;
	}

	public String getName() {
		return name;
	}
}

public abstract class Direction3 {
	// 创建几个实例
	public static final Direction3 FRONT = new Direction3("前") {
		@Override
		public void show() {
			System.out.println("前");
		}

	};
	public static final Direction3 BEHIND = new Direction3("后") {
		@Override
		public void show() {
			System.out.println("后");
		}

	};
	public static final Direction3 LEFT = new Direction3("左") {
		@Override
		public void show() {
			System.out.println("左");
		}

	};
	public static final Direction3 RIGHT = new Direction3("右") {
		@Override
		public void show() {
			System.out.println("右");
		}

	};

	// 构造私有，别人就不能无限的创建了
	// private Direction2() {
	// }

	// 加入成员变量,并去掉无参构造
	private String name;

	private Direction3(String name) {
		this.name = name;
	}

	public String getName() {
		return name;
	}

	// 加入抽象方法
	public abstract void show();
}

public class DirectionDemo {
	public static void main(String[] args) {
		Direction d = Direction.FRONT;
		System.out.println(d); // cn.itcast_01.Direction@175078b
		System.out.println("------------------------------------");
		Direction2 d2 = Direction2.FRONT;
		System.out.println(d2);// cn.itcast_01.Direction2@11563ff
		System.out.println(d2.getName());
		d2 = Direction2.RIGHT;
		System.out.println(d2);
		System.out.println(d2.getName());
		System.out.println("------------------------------------");
		Direction3 d3 = Direction3.FRONT;
		System.out.println(d3);
		System.out.println(d3.getName());
		d3.show();


		d3 = Direction3.LEFT;
		System.out.println(d3);
		System.out.println(d3.getName());
		d3.show();
	}
}

可变参数

枚举

/*
 * 通过JDK5提供的枚举来做枚举类
 */
public enum Direction {
	FRONT, BEHIND, LEFT, RIGHT;
}

/*
 * 通过JDK5提供的枚举来做枚举类
 */
public enum Direction2 {
	FRONT("前"), BEHIND("后"), LEFT("左"), RIGHT("右");


	private String name;


	private Direction2(String name) {
		this.name = name;
	}


	public String getName() {
		return name;
	}


	// @Override
	// public String toString() {
	// return "我爱林青霞";
	// }
}

/*
 * 通过JDK5提供的枚举来做枚举类
 */
public enum Direction3 {
	FRONT("前") {
		@Override
		public void show() {
			System.out.println("前");
		}
	},
	BEHIND("后") {
		@Override
		public void show() {
			System.out.println("后");
		}
	},
	LEFT("左") {
		@Override
		public void show() {
			System.out.println("左");
		}
	},
	RIGHT("右") {
		@Override
		public void show() {
			System.out.println("右");
		}
	};

	private String name;

	private Direction3(String name) {
		this.name = name;
	}

	public String getName() {
		return name;
	}

	public abstract void show();
}

public class DirectionDemo {
	public static void main(String[] args) {
		Direction d = Direction.FRONT;
		System.out.println(d); // FRONT
		// public String toString()返回枚举常量的名称，它包含在声明中。
		System.out.println("-------------");
		Direction2 d2 = Direction2.FRONT;
		System.out.println(d2);
		System.out.println(d2.getName());
		System.out.println("-------------");
		Direction3 d3 = Direction3.FRONT;
		System.out.println(d3);
		System.out.println(d3.getName());
		d3.show();
		System.out.println("--------------");


		Direction3 dd = Direction3.FRONT;
		dd = Direction3.LEFT;


		switch (dd) {
		case FRONT:
			System.out.println("你选择了前");
			break;
		case BEHIND:
			System.out.println("你选择了后");
			break;
		case LEFT:
			System.out.println("你选择了左");
			break;
		case RIGHT:
			System.out.println("你选择了右");
			break;
		}
	}
}

public class EnumMethodDemo {
	public static void main(String[] args) {
		// int compareTo(E o)
		Direction2 d21 = Direction2.FRONT;
		Direction2 d22 = Direction2.BEHIND;
		Direction2 d23 = Direction2.LEFT;
		Direction2 d24 = Direction2.RIGHT;
		System.out.println(d21.compareTo(d21));
		System.out.println(d21.compareTo(d24));
		System.out.println(d24.compareTo(d21));
		System.out.println("---------------");
		// String name()
		System.out.println(d21.name());
		System.out.println(d22.name());
		System.out.println(d23.name());
		System.out.println(d24.name());
		System.out.println("--------------");
		// int ordinal()
		System.out.println(d21.ordinal());
		System.out.println(d22.ordinal());
		System.out.println(d23.ordinal());
		System.out.println(d24.ordinal());
		System.out.println("--------------");
		// String toString()
		System.out.println(d21.toString());
		System.out.println(d22.toString());
		System.out.println(d23.toString());
		System.out.println(d24.toString());
		System.out.println("--------------");
		// <T> T valueOf(Class<T> type,String name)
		Direction2 d = Enum.valueOf(Direction2.class, "FRONT");
		System.out.println(d.getName());
		System.out.println("----------------");
		// values()
		// 此方法虽然在JDK文档中查找不到，但每个枚举类都具有该方法，它遍历枚举类的所有枚举值非常方便
		Direction2[] dirs = Direction2.values();
		for (Direction2 d2 : dirs) {
			System.out.println(d2);
			System.out.println(d2.getName());
		}
	}
}

(2)JDK6(了解)
(3)JDK7(理解)
二进制的表现形式
用_分隔数据
switch语句可是用字符串
泛型推断(菱形泛型)
多catch的使用

自动释放资源的用法

import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.util.ArrayList;

public class Demo {
	public static void main(String[] args) {
		// 二进制字面量
		int x = 0b100101;
		System.out.println(x);
		// 数字字面量可以出现下划线
		int y = 1_1123_1000;
		// 不能出现在进制标识和数值之间
		int z = 0x111_222;
		// 不能出现在数值开头和结尾
		int a = 0x11_22;
		// 不能出现在小数点旁边
		double d = 12.3_4;
		// switch 语句可以用字符串?自己回顾
		// 泛型简化
		ArrayList<String> array = new ArrayList<>();
		// 异常的多个catch合并
		method();
	}

	private static void method() {
		// try-with-resources 语句
		// try(必须是java.lang.AutoCloseable的子类对象){…}

		try {
			FileReader fr = new FileReader("a.txt");
			FileWriter fw = new FileWriter("b.txt");
			int ch = 0;
			while ((ch = fr.read()) != -1) {
				fw.write(ch);
			}
			fw.close();
			fr.close();
		} catch (IOException e) {
			e.printStackTrace();
		}

		// 改进版的代码
		try (FileReader fr = new FileReader("a.txt");
				FileWriter fw = new FileWriter("b.txt");) {
			int ch = 0;
			while ((ch = fr.read()) != -1) {
				fw.write(ch);
			}
		} catch (IOException e) {
			e.printStackTrace();
		}
	}
}

(4)JDK8(了解)
可以去网上了解资料

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