1.Math
package com.yfs.javase;
public class MathDemo {
public static void main(String[] args) {
int r = 2;
System.out.println("圆的面积 : " + (Math.PI * r * r));
System.out.println("半径的平方 : " + (Math.pow(r, 2)));
System.out.println("16的平方根 : " + (Math.sqrt(16)));
System.out.println("随机数 ： " + Math.random());
System.out.println("Math.round(3.4) ： " + Math.round(3.4));
System.out.println("Math.round(3.5) ： " + Math.round(3.5));
System.out.println("Math.ceil(3.1) ： " + Math.ceil(3.1));
System.out.println("Math.ceil(3.7) ： " + Math.ceil(3.7));
System.out.println("Math.floor(3.1) ： " + Math.floor(3.1));
System.out.println("Math.floor(3.7) ： " + Math.floor(3.7));
}
}
2.String
package com.yfs.javase;
public class StringDemo {
public static void main(String[] args) {
String s1 = " Hello World hello Java I like JAVA you like jAVA ";
System.out.println("s1： " + s1);
System.out.println("s1的长度： " + s1.length());
//去空格
s1 = s1.trim();
System.out.println("s1的长度： " + s1.length());
System.out.println("s1: " + s1);
System.out.println("s1第一个字符: " + s1.charAt(0));
System.out.println("s1最后一个字符: " + s1.charAt(47));
//查找
System.out.println("s1大写 : " + s1.toUpperCase());
System.out.println("s1小写 : " + s1.toLowerCase());
System.out.println("s1是否包含'java' : " + s1.contains("java"));
System.out.println("s1是否包含'java' : " + s1.toLowerCase().contains("java"));
//查找索引
System.out.println("s1.indexOf('java') : " + s1.toLowerCase().indexOf("java"));
System.out.println("s1.indexOf('java',19) : " + s1.toLowerCase().indexOf("java",19));
System.out.println("s1.lastIndexOf('java') : " + s1.toLowerCase().lastIndexOf("java"));
//比较
String s2 = new String("aBc");
String s3 = new String("abC");
System.out.println("s2.equals(s3) : " + s2.equals(s3));
System.out.println("s2.equalsIgnoreCase(s3) : " + s2.equalsIgnoreCase(s3));
System.out.println("s3.compareTo(s2) : " + s3.compareTo(s2));
System.out.println("s2.compareToIgnoreCase(s3) : " + s2.compareToIgnoreCase(s3));
//包含字符
String s4 = "C:\javase\Hello.java";
System.out.println("s4在c盘？" + s4.startsWith("C:"));
System.out.println("s4是否java文件？" + s4.endsWith(".java"));
//截取
s4 = s1.substring(18);
System.out.println("s4 = " + s4);
System.out.println("s1.substring(6,11) = " + s1.substring(6,11));
s4 = "2014-7-1";
String[] as = s4.split("-");
for (int i = 0; i < as.length; i++) {
System.out.println(as[i]);
}
//替换
System.out.println(s1.replace("l", "*"));
int a = 15;
String s5 = String.valueOf(a);//类型转换
}
}
3.Integer
package com.yfs.javase;
public class WrapDemo {
public static void main(String[] args) {
int a = 15;
//a.toString();
//包装
Integer o1 = new Integer(a);//整型对象
String s1 = o1.toString();
System.out.println("s1 = " + s1);
//访问属性
System.out.println("最大值： " + Integer.MAX_VALUE);
int b = 15;
Integer o2 = new Integer(b);
System.out.println("o1 == o2 ? " + (o1 == o2));//比较对象
System.out.println("a == b ? " + (a == b));//比较数值
Integer o3 = 15;//自动装箱机制new Integer(15);
System.out.println("o3 = " + o3);
System.out.println("o3 == b ? " + (o3 == b));//自动拆箱
a = o3;//自动拆箱 65 97
char c = 'z';
Character oc = new Character(c);
System.out.println("oc.compareTo('Z') : " + oc.compareTo('Z'));
}
}