我来弄些财富呵呵10.常用类.ppt

Java面向对象程序设计,-数组,2,本节内容,字符串操作类 java.lang.String类 构造方法 java.lang.StringBuffer类 java.util.StringTokenizer类 不同的应用场合,3,String类的构造方法,生成空字符串 public String() 从byte数组生成(0127) public String(byte bytes) public String(byte bytes, int offset, int length) public String(byte bytes, Charset charset) public String(byte bytes, int offset, int length， Charset charset) public String(byte bytes, String charsetName) ascii,utf-8,iso-8859-1,utf-16 public String(byte bytes, int offset, int length， String charsetName),String类的构造方法,从char数组生成 public String(char value) public String(char value, int offset, int length) 从int数组生成 public String(int codePoints， int offset, int code) 1114111 从字符串生成 public String(String original) public String(StringBuffer buffer) public String(StringBuilder builder),5,String类的构造方法,java.lang.String类字符串/字符序列 构造方法的使用,String a=“abc“; String b=new String(); b=“abc“; String c=new String(a); String d=new String(“abc“); byte bytes=97,98,99; String e=new String(bytes); String f=new String(bytes,0,3); char value=a,b,c; String g=new String(value); int codePoint=97,98,99; String h=new String(codePoint,0,3);,a=abc; b=abc; c=abc; d=abc; e=abc; f=abc; g=abc; h=abc;,6,String类的构造方法,java.lang.String类字符串/字符序列 构造方法的使用,class Demo3 public static void main (String args) try byte bytes=97,98,99; String a=new String(bytes,“ascii“); System.out.println(“a=“+a); String b=new String(bytes,“utf-8“); System.out.println(“b=“+b); catch(Exception e) System.out.println(e); ,String类的比较方法,public boolean equals(Object anObject) 判断是否是同一个对象，是ture；然后anObject是否为一个字符串对象，否false；是判断是否内容相同 public boolean equalsIgnoreCase(String anotherString) 判断逻辑与equals相同，仅仅在判断内容上不考虑大小写 public int compareTo(Object o) 若o不是字符串对象，则抛错；若是则调用下面的函数 public int compareTo(String anotherString) 判断两个字符串的内容是否相同，是0；否不等于0的整数 public int compareToIgnoreCase(String str) 基本功能同上，仅仅在判断时不考虑大小写,class Demo4 public static void main (String args) String a=“abc“; String b=“abc“; String c=“ABC“; System.out.println(“a.equals(b)=“+a.equals(b); System.out.println(“a.equals(c)=“+a.equals(c); System.out.println(“a.equalsIgnoreCase(c)=“+a.equals(c); System.out.println(“pareTo(b)=“+pareTo(b); System.out.println(“pareTo(c)=“+pareTo(c); System.out.println(“pareToIgnoreCase(c)=“+pareTo(c); ,运行结果： a.equals(b)=true; a.equals(c)=false; a.equalsIgnoreCase(c)=true pareTo(b)=0 pareTo(c)=32 pareToIgnoreCase(c)=0,8,String类的取字符或子串方法,获取长度 public int length() 字符串的长度，即包含多少个字符 获取特定子串(substring)和字符 public String substring(int beginIndex) public String substring(int beginIndex, int endIndex) beginIndex: 起始索引位置(包含) endIndex: 结束索引位置(不包含) public char charAt(int index),String s1 = “java语言“; String s2 = “JavA语言“; System.out.println(s1.length(); System.out.println(s2.length(); System.out.println(s1.substring(0, 4); System.out.println(s1.substring(4); System.out.println(s2.substring(0, 4); System.out.println(s2.substring(4); System.out.println(s1.charAt(0);,运行结果： 6 6 java 语言 JavA 语言 j,9,字符串操作类,java.lang.String类字符串/字符序列 字符串前缀(prefix)/后缀(suffix)的判断 public boolean startsWith(String prefix) 判断字符串是否以一特定的字符串开头 public boolean startsWith(String prefix, int toffset) public boolean endsWith(String suffix) 判断字符串是否以一特定的字符串结束,class Demo5 public static void main (String args) String a=“abc“; System.out.println(“a.startsWith(“ab“)=“+a.startsWith(“ab“); System.out.println(“a.startsWith(“bc“,1)=“+a.startsWith(“bc“,1); System.out.println(“a.endsWith(“e“)=“+a.endsWith(“c“); ,a.startsWith(“ab”)=true; a.startsWith(“b”,1)=true; a.endsWith(“e”)=true;,10,String类查询字符/字符串,public int indexOf(int ch) 该字符在字符串中第一次出现位置的索引值；否则返回-1 public int indexOf(int ch, int fromIndex) public int indexOf(String str) public int indexOf(String str, int fromIndex) public int lastIndexOf(int ch) public int lastIndexOf(int ch, int fromIndex) public int lastIndexOf(String str) public int lastIndexOf(String str, int fromIndex),11,字符串操作类,java.lang.String类字符串/字符序列 方法举例,String s = “java语言”; System.out.println(s.indexOf(a); System.out.println(s.indexOf(a, 2); System.out.println(s.indexOf(“a”); System.out.println(s.indexOf(“语言”); System.out.println(s.lastIndexOf(a); System.out.println(s.lastIndexOf(v, 1); System.out.println(s.lastIndexOf(“语言”); System.out.println(s.lastIndexOf(“v”, 2);,运行结果： 1 3 1 4 3 -1 4 2,12,字符串操作类,java.lang.String类字符串/字符序列 字符串转变为数组 public byte getBytes() 将字符串转变为一个字节数组 public byte getBytes(String charsetName) throws UnsupportedEncodingException 按特定的字符编码格式将字符串转变为一个字节数组 public char toCharArray() 将字符串转变为一个字符数组,13,字符串操作类,java.lang.String类字符串/字符序列 方法举例,String s = “java语言“; char c = s.toCharArray(); System.out.println(c.length); byte b = s.getBytes(); System.out.println(b.length); b = s.getBytes(“ISO8859-1“); System.out.println(b.length);,运行结果： 6 8 6,中文Windows操作系统: 默认字符集 GB2312 其他系统: 默认字符集 ISO-8859-1,14,String类的其他方法,public String concat(String str) 连接字符串 “cares“.concat(“s“) returns “caress“ “to“.concat(“get“).concat(“her“) returns “together“ public String replace(char oldChar, char newChar) 在字符串中进行字符替换 “mesquite in your cellar“.replace(e, o) returns “mosquito in your collar” “JonL“.replace(q, x) returns “JonL“ (no change),String类的基本数据转换方法,static String valueOf(boolean b); static String valueOf(char c); static String valueOf(char data); static String valueOf(char data, int offset, int count); static String valueOf(double d); static String valueOf(float f); static String valueOf(int i); static String valueOf(long l); static String valueOf(Object obj);,class Demo6 public static void main (String args) boolean bo=true; char c=a; char chars=a,b,c; byte b=1; int i=123456; long l=1234567890l; float f=0.123f; double d=0.456; System.out.println(“valueOf(boolean)=“+String.valueOf(bo); System.out.println(“valueOf(char)=“+String.valueOf(c); System.out.println(“valueOf(chars)=“+String.valueOf(chars); System.out.println(“valueOf(chars,0,2)=“+String.valueOf(chars,0,2); System.out.println(“valueOf(byte)=“+String.valueOf(b); System.out.println(“valueOf(int)=“+String.valueOf(i); System.out.println(“valueOf(long)=“+String.valueOf(l); System.out.println(“valueOf(float)=“+String.valueOf(f); System.out.println(“valueOf(double)=“+String.valueOf(d); ,valueOf(boolean)=true; valueOf(char)=a; valueOf(chars)=abc; valueOf(chars,0,2)=ab; valueOf(byte)=1; valueOf(int)=123456; valueOf(long)=1234567890; valueOf(float)=0.123; valueOf(double)=0.456,16,字符串操作类,java.lang.StringBuffer类 一个可变(mutable)/动态的字符序列 构造方法 public StringBuffer() public StringBuffer(String str) 主要方法 添加(append)和插入(insert, 指定位置) public StringBuffer append(boolean b) public StringBuffer insert(int offset, boolean b) boolean, char, char, double, float, int, long, String 转换为字符串 - public String toString(),17,字符串操作类,java.lang.StringBuffer类方法举例,String s = “java语言“; StringBuffer buffer = new StringBuffer(s); buffer.append(“easy ”); buffer.insert(6, “ is “); buffe.append(true); buffe.append(2); s = buffer.toString(); System.out.println(s);,运行结果： java语言 is easy true2,18,字符串操作类,字符串的连接运算(Concatenation) “java”和“语言” String s = “java” + “语言”; String s = “java”.concat(“语言”); StringBuffer buffer = new StringBuffer(“java”); buffer.append(“语言”); String s = buffer.toString(); 常用第1种和第3种方法,19,字符串操作类,字符串的连接运算(Concatenation) +与append方法比较,class MyTimer private final long start; public MyTimer() start = System.currentTimeMillis(); public long getElapsed() return System.currentTimeMillis() - start; ,public class AppDemo static final int N = 47500; public static void main(String args) MyTimer mt = new MyTimer(); String str1 = “; for (int i = 1; i = N; i+) str1 = str1 + “*“; System.out.println(“#1s time = “ + mt.getElapsed(); mt = new MyTimer(); StringBuffer s