简单的函数重载，int等的数值范围

public class OverloadDemo {

	static void f(float d) {
		System.out.println("the argument is float");

	}	static void f(double d) {
		System.out.println("the argument is double");

	}

	static void f(float d, double s) {
		System.out.println("the argument is float and double");
	}

	static void f(double d, float s) {
		System.out.println("the argument is double  and float");
	}

	public static void main(String[] args) {

		OverloadDemo.f(2); // 如果第一个方法的参数可以赋值给第二个参数，而第二个不能赋值给，就用第一个方法
		// OverloadDemo.f(2, 3); 编译出错，有二义性
	}

}

执行结果：
the argument is float
因为float型变量可以赋值给double，反之却不成立，故调用红色部分的函数
2，计算int，byte，double，float的最大值和最小值

import java.util.StringTokenizer;

public class MaxVaules {

	private static final byte MAX_BYTE = Byte.MAX_VALUE;
	private static final byte MIN_BYTE = Byte.MIN_VALUE;

	private static final int MAX_INT = Integer.MAX_VALUE;
	private static final int MIN_INT = Integer.MIN_VALUE;

	private static final double MAX_DOUBLE = Double.MAX_VALUE;
	private static final double MIN_DOUBLE = Double.MIN_VALUE;

	private static final float MAX_FLOAT = Float.MAX_VALUE;
	private static final float MIN_FLOAT = Float.MIN_VALUE;

	public static void main(String[] args) {

		System.out.println(MaxVaules.MAX_BYTE); // 127
		System.out.println(MaxVaules.MIN_BYTE);// -128

		System.out.println(MaxVaules.MAX_INT); //
		System.out.println(MaxVaules.MIN_INT);

		System.out.println(MaxVaules.MAX_FLOAT); // 3.4*10^38
		System.out.println(MaxVaules.MAX_FLOAT);

		System.out.println(MaxVaules.MAX_DOUBLE);// 1.79*10^308
		System.out.println(MaxVaules.MIN_DOUBLE);

		String a = new String("hello");
		String b = "hello";
		System.out.println(a == b); // false

		float f = 4.2f;
		Float ff = new Float(4.2);
		System.out.println(f == ff); // true,自动拆箱

		int x = 19;
		int y = x << 1; // 相当于乘以2，内存紧张时可用移位操作
		System.out.println(y);
		y = x >> 1; // 除以2
		System.out.println(y);

		// String,StringBuffer,StringTokenizer
		String story = "A long time     ago";
		StringTokenizer st = new StringTokenizer(story); // 没有指定分隔符，用默认的空格为分隔符，多个空格算一个
		while (st.hasMoreElements())
			System.out.println(st.nextToken());

	}

}

结果如下：
127
-128
2147483647
-2147483648
3.4028235E38
3.4028235E38
1.7976931348623157E308
4.9E-324
false
true
38
9
A
long
time
ago