I、Java字符串
本节是一些Java中关于字符串处理的常用实例。
1.1 字符串比较
package example;
/*字符串比对*/
public class StringCompareEmp {
public static void main(String[] args) {
String str = "Hello World";
String anotherStr = "hello world";
Object objStr = str;
System.out.println(str.compareTo(anotherStr)); //返回第一个不等的差值
System.out.println(str.compareToIgnoreCase(anotherStr)); //忽略大小写
System.out.println(str.compareTo(objStr.toString()));
}
}
int compareTo(Object o)，int compareTo(String anotherString)，int compareToIgnoreCase(String str)这三个方法都是返回两个对比对象中第一个字符不等的字符差值。
1.2 查找字符串最后一次出现的位置
通过字符串函数strOrig.lastIndexOf(Stringname)来查找子字符串Stringname在strOrig出现的位置：
package example;
public class SearchlastString {
public static void main(String[] args) {
String strOrig = "Hello world, Hello Runoob";
String Stringname = "Runoob";
int lastIndex = strOrig.lastIndexOf(Stringname);
if (lastIndex == -1)
System.out.println("No find " + Stringname);
else
System.out.println(Stringname + "last at " + lastIndex);
}
}
1.3 删除字符串中的一个字符
通过字符串函数substring()来删除字符串中的一个字符，并将功能封装在removeCharAt()函数中：
package example;
public class RemoveString {
public static void main(String[] args) {
String str = "This is Java";
System.out.println(removeCharAt(str,3));
}
public static String removeCharAt(String s, int pos) {
return s.substring(0,pos) + s.substring(pos+1);
}
}
1.4 字符串替换
使用java String 类中的replace方法来替换字符串中的字符：
package example;
public class StringReplaceEmp {
public static void main(String[] args) {
String str = "Hello world";
System.out.println(str.replace('H', 'W'));
System.out.println(str.replaceFirst("He", "Wa"));
System.out.println(str.replaceAll("He", "Ha"));
}
}
1.5 字符串反转
使用Java的反转函数reverse()将字符串反转：
package example;
public class StringReverseEmp {
public static void main(String[] args) {
String string = "runoob";
String reverse = new StringBuffer(string).reverse().toString();
System.out.println("before reverse: " + string);
System.out.println("after reverse " + reverse);
}
}
1.6 字符串查找
使用String类的IndexOf()方法在字符串中查找子字符串出现的位置，如果存在返回字符串出现的位置：
package example;
public class SearchStringEmp {
public static void main(String[] args) {
String strOrig = "Google Runoob Taobao";
int intIndex = strOrig.indexOf("Runoob");
if (intIndex == -1) {
System.out.println("no find");
}
else {
System.out.println("at " + intIndex);
}
}
}
1.7 字符串分割
使用split()方法通过制定分隔符将字符串分割为数组：
package example;
public class StringSplitEmp {
public static void main(String[] args) {
String str = "www.baidu.com";
String[] temp;
String delimeter = "\\."; //分隔符, .需要进行转义
temp = str.split(delimeter);
for (int i = 0; i < temp.length; ++i) {
System.out.println(temp[i]);
}
}
}
1.8 字符串小写转大写
使用String toUpperCase()方法将字符串从小写转为大写：
package example;
public class StringToUpperCaseEmp {
public static void main(String[] args) {
String str = "string baidu";
String strUpper = str.toUpperCase();
System.out.println("Orignal: " + str);
System.out.println("ToUpper: " + strUpper);
}
}
1.9 测试两个字符串区域是否相等
使用regionMatch()方法检测两个字符串区域是否相等。
package example;
public class StringRegionMatch {
public static void main(String[] args) {
String first = "Welcome to Microsoft";
String second = "I work with microsoft";
//表示将first第11个字符与second第12个字符开始，比较9个字符
boolean match1 = first.regionMatches(11, second, 12, 9);
boolean match2 = first.regionMatches(true, 11, second, 12, 9); //第一个参数true表示忽略大小写
System.out.println("区分大小写的返回值： " + match1);
System.out.println("不区分大小写的返回值： " + match2);
}
}
1.10 字符串性能比较测试
通过两种方式创建字符串，测试其性能：
package example;
public class StringComparePerformance {
public static void main(String[] args) {
long startTime = System.currentTimeMillis();
for (int i = 0; i < 50000; ++i) {
String s1 = "hello";
String s2 = "hello";
}
long endTime = System.currentTimeMillis();
System.out.println("String关键字创建字符串 " + " : " + (endTime-startTime) + "ms");
long startTime2 = System.currentTimeMillis();
for (int i = 0; i < 50000; ++i) {
String s3 = new String("hello");
String s4 = new String("hello");
}
long endTime2 = System.currentTimeMillis();
System.out.println("String对象创建字符串" + " : " + (endTime2-startTime2) + "ms");
}
}
1.11 字符串格式化
使用format()方法来格式化字符串，还可以指定地区来格式化：
package example;
import java.util.*;
public class StringFormatEmp {
public static void main(String[] args) {
double e = Math.E;
System.out.format("%f%n", e);
System.out.format(Locale.CHINA, "%-10.4f%n%n", e); //指定本地为中国
}
}
1.12 连接字符串
通过+操作符和StringBuffer.append()方法来连接字符串，并比较其性能：
package example;
public class StringConcatenate {
public static void main(String[] args) {
long startTime = System.currentTimeMillis();
for (int i = 0; i < 5000; ++i) {
String result = "This is"
+ "testing the"
+ "difference " + "between"
+ "String" + "and" + "StringBuffer";
}
long endTime = System.currentTimeMillis();
System.out.println("使用+ ： " + (endTime-startTime) + "ms");
long startTime2 = System.currentTimeMillis();
for (int i = 0; i < 5000; ++i) {
StringBuffer result = new StringBuffer();
result.append("This is");
result.append("testig the");
result.append("dofference");
result.append("between");
result.append("String");
result.append("and");
result.append("StringBuffer");
}
long endTime2 = System.currentTimeMillis();
System.out.println("StringBuffer.append(): " + (endTime2-startTime2) + "ms");
}
}
II、数组
本节主要说明Java中对于数组的一些常用操作：
2.1 数组排序及元素查找
使用sort()方法对Java数组进行排序，使用binarySearch()方法查找数组中的元素，并使用自己定义的printArray()方法打印数组：
package example;
import java.util.Arrays;
public class SortArray {
public static void main(String[] args) throws Exception {
int array[] = {2,5,-2,6,-3,8,0,-7,-9,4};
Arrays.sort(array);
printArray("数组排序结果为： ", array);
int index = Arrays.binarySearch(array, 2);
System.out.println("元素2在第 " + index + " 个位置");
}
private static void printArray(String message, int array[]) {
System.out.println(message + ":[length: " + array.length + "]");
for (int i = 0; i < array.length; ++i) {
if (i != 0) {
System.out.print(", ");
}
System.out.print(array[i]);
}
System.out.println();
}
}
2.2 数组添加元素
使用sort()方法对Java数组进行排序，使用insertElement()方法向数组插入元素：
package example;
import java.util.Arrays;
public class ArrayInsert {
public static void main(String[] args) {
int array[] = {2,5,-2,6,-3,8,0,-7,-9,4};
Arrays.sort(array);
printArray("数组排序： " , array);
int index = Arrays.binarySearch(array, 1);
System.out.println("元素1所在的位置为（负数为不存在）： " + index);
int newIndex = -index - 1;
array = insertElement(array, 1, newIndex); //需要插入位置
printArray("数组添加元素1： " , array);
}
private static void printArray(String message, int array[]) {
System.out.println(message + ": [length: " + array.length + "]");
for (int i = 0; i < array.length; ++i) {
if (i != 0)
System.out.print(", ");
System.out.print(array[i]);
}
System.out.println();
}
private static int[] insertElement(int original[], int element, int index) {
int length = original.length;
int destination[] = new int[length+1];
System.arraycopy(original, 0, destination, 0, index);
destination[index] = element;
System.arraycopy(original, index, destination, index+1, length-index);
return destination;
}
}
2.3 获取数组长度
使用数组属性length获取数组长度。
package example;
public class ArrayLengthEmp {
public static void main(String[] args) {
int[][] array = { {1,2,3}, {4,5,6}, {7,8,9}, {0,5,3} };
System.out.println(array.length);
System.out.println(array[0].length);
}
}
2.4 数组反转
使用Collections.reverse(ArrayList)将数组进行反转：
package example;
import java.util.ArrayList;
import java.util.Collections;
public class ArrayReverseEmp {
public static void main(String[] args) {
ArrayList<String> arrayList = new ArrayList<String>();
arrayList.add("A");
arrayList.add("B");
arrayList.add("C");
arrayList.add("D");
arrayList.add("E");
System.out.println("反转前： " + arrayList);
Collections.reverse(arrayList);
System.out.println("反转后： " + arrayList);
}
}
2.5 数组后去最大和最小值
使用Collections.max()和Collections.min()方法查找数组中的最大和最小值：
package example;
import java.util.Arrays;
import java.util.Collections;
public class ArrayMaxMin {
public static void main(String[] args) {
Integer[] numbers = {8,2,7,1,4,9,5};
int min = (int)Collections.min(Arrays.asList(numbers));
int max = (int)Collections.max(Arrays.asList(numbers));
System.out.println("Max: " + max);
System.out.println("Min: " + min);
}
}
2.6 数组合并
通过List类的Arrays.toString()方法和List类的list.Addall(array1.asList(array2))方法将两个数组合并为一个数组：
package example;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
public class ArrayMerge {
public static void main(String[] args) {
String a[] = {"A", "E", "I" };
String b[] = {"O", "U" };
List list = new ArrayList(Arrays.asList(a));
list.addAll(Arrays.asList(b));
Object[] c = list.toArray();
System.out.println(Arrays.toString(c));
}
}
2.7 数组填充
使用Arrays.fill(arrayname, value)方法和Arrays.fill(arrayname, starting index, ending index, value)方法向数组中填充元素：
package example;
import java.util.*;
public class ArrayFillEmp {
public static void main(String[] args) {
int array[] = new int[6];
Arrays.fill(array, 100);
for (Integer a : array)
System.out.printf("%d,", a);
System.out.println();
Arrays.fill(array, 3, 6, 50);
for (Integer a : array)
System.out.printf("%d,", a);
}
}
2.8 数组扩容
在数组初始化后对数组进行扩容：
package example;
public class ArrayExtendEmp {
public static void main(String[] args) {
String[] names = new String[] {"A", "B", "C"};
String[] extended = new String[5];
extended[3] = "D";
extended[4] = "E";
System.arraycopy(names, 0, extended, 0, names.length);
for (String str : extended) {
System.out.println(str);
}
}
}
2.9 删除数组元素
使用remove()方法来删除数组元素：
package example;
import java.util.ArrayList;
public class ArrayRemoveEmp {
public static void main(String[] args) {
ArrayList<String> objArray = new ArrayList<String>();
objArray.clear();
objArray.add(0,"第0个元素");
objArray.add(1,"第1个元素");
objArray.add(2,"第2个元素");
System.out.println("Before Remove: " + objArray);
objArray.remove(1);
objArray.remove("第0个元素");
System.out.println("After Remove: " + objArray);
}
}
2.10 数组差集
使用removeAll()方法计算两个数组的差集：
package example;
import java.util.ArrayList;
public class ArrayDifferenceSetEmp {
public static void main(String[] args) {
ArrayList objArray = new ArrayList();
ArrayList objArray2 = new ArrayList();
objArray2.add(0,"common1");
objArray2.add(1,"common2");
objArray2.add(2,"notcommon");
objArray2.add(3,"notcommon1");
objArray.add(0,"common1");
objArray.add(1,"common2");
objArray.add(2,"notcommon2");
System.out.println("array1 的元素： " + objArray);
System.out.println("array2的元素： " + objArray2);
objArray.removeAll(objArray2);
System.out.println("array1与array2数组的差集为： " + objArray);
}
}
2.11 数组交集
使用retainAll()方法计算两个数组的交集：
package example;
import java.util.ArrayList;
public class ArrayIntersectionEmp {
public static void main(String[] args) {
ArrayList objArray = new ArrayList();
ArrayList objArray2 = new ArrayList();
objArray2.add(0, "common1");
objArray2.add(1, "common2");
objArray2.add(2, "notcommon");
objArray2.add(3, "notcommon1");
objArray.add(0, "common1");
objArray.add(1, "common2");
objArray.add(2, "notcommon2");
System.out.println("array1 数组元素： " + objArray);
System.out.println("array2 数组元素： " + objArray2);
objArray.retainAll(objArray2);
System.out.println("array2 & array1: " + objArray);
}
}
2.12 数组中查找指定元素
使用contain()方法查找数组中的指定元素：
package example;
import java.util.ArrayList;
public class ArrayContainEmp {
public static void main(String[] args) {
ArrayList objArray = new ArrayList<String>();
ArrayList objArray2 = new ArrayList<String>();
objArray2.add("common1");
objArray2.add("common2");
objArray2.add("notcommon");
objArray2.add("notcommon1");
objArray.add("common1");
objArray.add("common2");
System.out.println("objArray: " + objArray);
System.out.println("objArray2: " + objArray2);
System.out.println("objArray是否包含common2？ " + objArray.contains("common2"));
System.out.println("objArray2是否包含数组objArray? " + objArray2.contains(objArray));
}
}
2.13 判断数组是否相等
使用equals()方法判断数组是否相等：
package example;
import java.util.Arrays;
public class ArrayEqualsEmp {
public static void main(String[] args) {
int[] ary = {1,2,3,4,5,6};
int[] ary1 = {1,2,3,4,5,6};
int[] ary2 = {1,2,3,4};
System.out.println("ary == ary1 ? " + Arrays.equals(ary, ary1));
System.out.println("ary1 == ary2 ? " + Arrays.equals(ary1, ary2));
}
}
2.14 数组并集
使用union()方法计算数组并集：
package example;
import java.util.Set;
import java.util.HashSet;
public class ArrayUnionEmp {
public static void main(String[] args) throws Exception {
String[] arr1 = { "1", "2", "3" };
String[] arr2 = { "4", "5", "6" };
String[] result_union = union(arr1, arr2);
System.out.println("Union: ");
for (String str : result_union)
System.out.println(str);
}
public static String[] union(String[] arr1, String[] arr2) {
Set<String> set = new HashSet<String>();
for (String str : arr1) {
set.add(str);
}
for (String str : arr2) {
set.add(str);
}
String[] result = {};
return set.toArray(result);
}
}
【参考】
[1] Java实例
