String、StringBuffer、StringBuilder、Math学习笔记

* 不可变的String类 final String
* +-->字符串连接符以及将其他对象转为字符串的特殊支持
*  比较、查找、复制、提取、转换、检查 操作

* StringBuffer-->可变的字符序列 线程安全的字符缓冲区
* 在字符串缓冲区进行同步
* 主要操作是-->append(将字符添加到缓冲区末尾)
* 			insert(将字符添加到指定位置)
*
* StringBuilder-->可变字符序列
*  但不保证同步，需外部同步
*  属于StringBuffer的简易版本
*  主要操作与StringBuffer一致

* Math类用于执行基本的数学运算
* Math 类包含用于执行基本数学运算的方法，如初等指数、对数、平方根和三角函数

package com.undergrowth.lang;

import java.io.UnsupportedEncodingException;
import java.nio.charset.Charset;
import java.util.Locale;
import java.util.Map;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

import org.junit.Test;

/**
* 不可变的String类 final String
* +-->字符串连接符以及将其他对象转为字符串的特殊支持
*  比较、查找、复制、提取、转换、检查 操作
*
* @author Administrator
*
*/
public class StringLearn {

public StringLearn() {
// TODO Auto-generated constructor stub
}

/**
* 获取系统所有字符集
*/
@Test
public void testAvailCharset() {
Map<String, Charset> charsetMap = Charset.availableCharsets();
System.out.println("总共有字符集:" + charsetMap.size());
System.out.println("默认字符集为:" + Charset.defaultCharset().displayName());
System.out.println("遍历支持字符集如下:");
for (Map.Entry<String, Charset> charsetEntry : charsetMap.entrySet()) {
System.out.println(charsetEntry.getKey() + ":"
+ charsetEntry.getValue().displayName() + "\t"
+ charsetEntry.getValue().name());
}

}

/**
* 显示系统支持的语言相关的政治、地理、文化区域 系统支持的语言环境
*/
@Test
public void testAvailLocale() {
Locale[] locales = Locale.getAvailableLocales();
for (Locale locale : locales) {
System.out.println(locale.getCountry() + "\t"
+ locale.getDisplayCountry() + "\t"
+ locale.getDisplayName() + "\t" + locale.getLanguage()
+ "\t" + locale.getDisplayLanguage());
}
}

// 测试字符串
String testString = "123@987@,qwert:@op";
// 测试比较字符串
String otherTestString = "123@987@,QWERT:@op";
// 测试字符数组
char[] testCharArray = testString.toCharArray();

/**
* 测试字符串的查找功能
*/
@Test
public void testLook() {
System.out.println("待测试字符串为:" + testString);
// 获取最后一个字符
System.out.println("testString.charAt(testString.length()-1)-->"
+ testString.charAt(testString.length() - 1));
System.out.println("testString.codePointAt(testString.length()-1)-->"
+ testString.codePointAt(testString.length() - 1));
System.out
.println("testString.codePointBefore(testString.length()-1)-->"
+ testString.codePointBefore(testString.length() - 1));
System.out
.println("testString.codePointCount(testString.length()-2, testString.length())-->"
+ testString.codePointCount(testString.length() - 2,
testString.length()));
// 查找索引
System.out.println(testString.indexOf("qw"));
System.out.println(testString.indexOf("qw", 3));
System.out.println(testString.lastIndexOf("@"));
System.out.println(testString.lastIndexOf("@", 3));
// 长度
System.out.println(testString.length());
System.out.println(testString.offsetByCodePoints(2, 5));
}

/**
* 测试字符串比较
*/
@Test
public void testComparable() {
System.out.println(otherTestString.compareTo(testString));
System.out.println(otherTestString.compareToIgnoreCase(testString));
System.out.println(otherTestString.equals(testString));
System.out.println(otherTestString.equalsIgnoreCase(testString));
// 正则表达式进行匹配
testString = "12345@qwert";
String regex = "[0-9]{1,}@[a-z]{1,}";
System.out.println(testString.matches(regex));
// 正则表达式匹配
Pattern pattern = Pattern.compile(regex);
Matcher matcher = pattern.matcher(testString);
System.out.println(matcher.matches());
testString = "123@987@,qwert:@op";
// 区域匹配
System.out.println(testString.regionMatches(0, otherTestString, 0,
testString.length()));
System.out.println(testString.regionMatches(0, otherTestString, 0, 7));
}

/**
* 测试字符串复制
*/
@Test
public void testCopy() {
System.out.println(otherTestString.concat(testString));
System.out.println(String.copyValueOf(testCharArray));
System.out.println(String.copyValueOf(testCharArray, 2, 5));
// 复制到字符数组
char[] dst = new char[1024];
testString.getChars(0, testString.length(), dst, 5);
System.out.println(dst);
// 字符串的内部规范化表示
System.out.println(testString.intern());
}

/**
* 字符串检查
*/
@Test
public void testCheck() {
System.out.println(otherTestString.contains(testString));
System.out.println(otherTestString.contentEquals(testString));
// 结束
System.out.println(testString.endsWith("op"));
System.out.println(testString.endsWith("oP"));
// 是否为空
System.out.println(testString.isEmpty());
// 开头
System.out.println(testString.startsWith("23"));
System.out.println(testString.startsWith("123"));
System.out.println(testString.startsWith("@", 3));
}

/**
* 测试字符串转换
*
* @throws UnsupportedEncodingException
*/
@Test
public void testTransform() throws UnsupportedEncodingException {
// String的静态方法进行转换
System.out.println(String.format(testString));
System.out.println(String.format(testString + "\t %d %o %x", 100, 100,
100));
System.out.println(String.format(Locale.CANADA, "你好," + testString
+ "\t %d %o %x", 100, 100, 100));
// 默认采用GBK字符集获取字节码
System.out.println(testString.getBytes());
System.out.println(testString.getBytes(Charset.forName("UTF-8")));
System.out.println(testString.getBytes("ISO-8859-1"));
// 转换为小写、大写
System.out.println(otherTestString.toLowerCase());
System.out.println(testString.toUpperCase());
// 去除空白
System.out
.println(String.valueOf("  " + otherTestString + "  ").trim());
System.out.println(String.valueOf(12.367));
}

/**
* 字符串提取操作
*/
@Test
public void testExtract() {
// 替换
System.out.println(testString.replace("@", "连接符"));
System.out.println(testString.replaceFirst("@", "连接符"));
// 分割
String[] testArrayStrings = testString.split("@");
for (String string : testArrayStrings) {
System.out.println(string);
}
// 截取
System.out.println(testString.substring(3));
System.out.println(testString.substring(3, 6));
}

}

package com.undergrowth.lang;

import org.junit.Test;

/**
* StringBuffer-->可变的字符序列 线程安全的字符缓冲区
* 在字符串缓冲区进行同步
* 主要操作是-->append(将字符添加到缓冲区末尾)
* 			insert(将字符添加到指定位置)
*
* StringBuilder-->可变字符序列
*  但不保证同步，需外部同步
*  属于StringBuffer的简易版本
*  主要操作与StringBuffer一致
*
* @author Administrator
*
*/
public class StringBufferBuilderLearn {

String str = "测试StringBuffer字符串 ";
StringBuffer sbBuffer = new StringBuffer();
StringBuffer sbBuffer2 = new StringBuffer(30);
StringBuffer sbBuffer3 = new StringBuffer(str);

public StringBufferBuilderLearn() {
// TODO Auto-generated constructor stub

}

/**
* 测试长度与容量
*/
@Test
public void testLength() {
System.out.println(sbBuffer.capacity());
System.out.println(sbBuffer.length());
System.out.println(sbBuffer2.capacity());
System.out.println(sbBuffer2.length());
System.out.println(sbBuffer3.capacity());
System.out.println(sbBuffer3.length());
//
sbBuffer2.ensureCapacity(50);
System.out.println(sbBuffer2.capacity());
System.out.println(sbBuffer2.length());
}

/**
* 测试Append-->附加到缓冲区末尾
*/
@Test
public void testAppend() {
System.out.println(sbBuffer.append(Boolean.TRUE).append('a')
.append(sbBuffer3));
}

/**
* 测试insert-->将字符添加到指定位置
*/
@Test
public void testInsert() {
System.out.println(sbBuffer3.insert(3, "插入字符"));
}

/**
* 查找方法与String的也很类似
*/
@Test
public void testLook() {
System.out.println(sbBuffer3);
System.out.println(sbBuffer3.charAt(5));
System.out.println(sbBuffer3.codePointAt(5));
System.out.println(sbBuffer3.codePointBefore(5));
// 获取字符数组
System.out.println(sbBuffer);
char[] dst = new char[1024];
sbBuffer3.getChars(0, sbBuffer3.length(), dst, 0);
System.out.println(sbBuffer.append(dst));
// 索引
System.out.println(sbBuffer3.indexOf("字符串"));
//
System.out.println(sbBuffer3);
System.out.println(sbBuffer3.lastIndexOf("你好"));
}

/**
* 测试删除字符操作
*/
@Test
public void testDelete() {
System.out.println(sbBuffer3);
System.out.println(sbBuffer3.deleteCharAt(5));
System.out.println(sbBuffer3.delete(1, 5));
}

/**
* 测试其他操作
*/
@Test
public void testOther() {
System.out.println(sbBuffer3.toString());
System.out.println(sbBuffer3.reverse());
System.out.println(sbBuffer3);
System.out.println(sbBuffer3.replace(0, 3, "替换字符串后的字符序列"));
System.out.println(sbBuffer3.substring(0, 10));
System.out.println(sbBuffer3);
System.out.println(sbBuffer3.capacity());
System.out.println(sbBuffer3.length());
sbBuffer3.trimToSize();
System.out.println(sbBuffer3.capacity());
System.out.println(sbBuffer3.length());
}
}

package com.undergrowth.lang;

import org.junit.Test;

/**
* Math类用于执行基本的数学运算
* Math 类包含用于执行基本数学运算的方法，如初等指数、对数、平方根和三角函数
* @author Administrator
*
*/
public class MathLearn {

public MathLearn() {
// TODO Auto-generated constructor stub
}

/**
* 测试Math的常量
*/
@Test
public void testMathConstant(){
System.out.println(Math.E);
System.out.println(Math.PI);
}

@Test
public void testMathMethod(){
//绝对值 Math.abs(-19)
System.out.println("绝对值 Math.abs(-19)");
System.out.println(Math.abs(-19));
System.out.println("绝对值 Math.abs(19)");
System.out.println(Math.abs(19));
//向上取整 Math.ceil(-19.1)
System.out.println("向上取整 Math.ceil(-19.1)");
System.out.println(Math.ceil(-19.1));
System.out.println("向上取整 Math.ceil(-19.8)");
System.out.println(Math.ceil(-19.8));
//立方根
System.out.println("立方根  Math.cbrt(9) x*x*x=9");
System.out.println(Math.cbrt(9));
//e的多少次幂
System.out.println("e的多少次幂 Math.exp(2)");
System.out.println(Math.exp(2));
//向下取整
System.out.println("向下取整 Math.floor(-19.2)");
System.out.println(Math.floor(-19.2));
System.out.println("向下取整 Math.floor(-19.7)");
System.out.println(Math.floor(-19.7));
//自然对数 e
System.out.println("自然对数 e Math.log(Math.E)");
System.out.println(Math.log(Math.E));
//10为底的指数
System.out.println("10为底的指数 Math.log10(10)");
System.out.println(Math.log10(10));
//最大数
System.out.println("最大数 Math.max(10, 20)");
System.out.println(Math.max(10, 20));
//最小数
System.out.println("最大数 Math.min(10, 20)");
System.out.println(Math.min(10, 20));
//第一个参数和第二参数之间的数 相邻
System.out.println(Math.nextAfter(20, 30));
System.out.println(Math.nextUp(20));
//幂
System.out.println("幂 Math.pow(10, 10)");
System.out.println(Math.pow(10, 10));
//随机数
System.out.println("随机数[0,1) Math.random()");
System.out.println(Math.random());
//四舍五入
System.out.println(Math.round(10.2));
System.out.println(Math.round(10.8));
System.out.println(Math.round(-10.2));
System.out.println(Math.round(-10.8));
//rint 最接近的整数
System.out.println(Math.rint(10.2));
System.out.println(Math.rint(10.6));
System.out.println(Math.rint(-10.2));
System.out.println(Math.rint(-10.6));
// f × 2scaleFactor
System.out.println(" f × 2scaleFactor Math.scalb(5, 2)");
System.out.println(Math.scalb(5, 2));
//参数的符号
System.out.println(Math.signum(98));
System.out.println(Math.signum(-98));
//sqrt
System.out.println(Math.sqrt(4));
}
}