如何在Java中声明动态字符串数组
我使用字符串数组声明为如何在Java中声明动态字符串数组,java,arrays,Java,Arrays,我使用字符串数组声明为zoom z[]=新字符串[422]。但是这个数组存储从0到32的值,所以在循环值32之后,我得到了空指针异常 如何用java解决这个问题 如何在java中声明动态数组?不,在java中无法使数组长度动态。您可以使用ArrayList或其他List实现。您希望使用or实现(例如,etc、or等),因为Java没有动态调整大小的数组 List<String> zoom = new ArrayList<>(); zoom.add("String 1");
zoom z[]=新字符串[422]代码>。但是这个数组存储从0
到32
的值,所以在循环值32
之后,我得到了空指针异常
如何用java解决这个问题
如何在java中声明动态数组?不,在java中无法使数组长度动态。您可以使用ArrayList
或其他List
实现。您希望使用or实现(例如,etc、or等),因为Java没有动态调整大小的数组
List<String> zoom = new ArrayList<>();
zoom.add("String 1");
zoom.add("String 2");
for (String z : zoom) {
System.err.println(z);
}
List zoom=new ArrayList();
缩放。添加(“字符串1”);
添加(“字符串2”);
用于(字符串z:缩放){
系统错误println(z);
}
编辑:
以下是一种更简洁的方法,可以使用以下命令使用任意数量的值初始化列表:
List zoom=Arrays.asList(“字符串1”、“字符串2”、“字符串n”);
也许您正在寻找向量。如果需要,它的容量会自动扩展。这不是最好的选择,但在简单的情况下也可以。值得您花时间阅读ArrayList
。您需要的是DefaultListModel-动态字符串列表变量
这里有一个使用DefaultListModel的完整类,就好像它是Delphi的TStringList一样。不同之处在于,您可以不受限制地向列表中添加字符串,并且您可以通过指定条目int来获得单个条目
文件名:StringList.java
package YOUR_PACKAGE_GOES_HERE;
//This is the StringList Class by i2programmer
//You may delete these comments
//This code is offered freely at no requirements
//You may alter the code as you wish
import java.io.File;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.swing.DefaultListModel;
public class StringList {
public static String OutputAsString(DefaultListModel list, int entry) {
return GetEntry(list, entry);
}
public static Object OutputAsObject(DefaultListModel list, int entry) {
return GetEntry(list, entry);
}
public static int OutputAsInteger(DefaultListModel list, int entry) {
return Integer.parseInt(list.getElementAt(entry).toString());
}
public static double OutputAsDouble(DefaultListModel list, int entry) {
return Double.parseDouble(list.getElementAt(entry).toString());
}
public static byte OutputAsByte(DefaultListModel list, int entry) {
return Byte.parseByte(list.getElementAt(entry).toString());
}
public static char OutputAsCharacter(DefaultListModel list, int entry) {
return list.getElementAt(entry).toString().charAt(0);
}
public static String GetEntry(DefaultListModel list, int entry) {
String result = "";
result = list.getElementAt(entry).toString();
return result;
}
public static void AddEntry(DefaultListModel list, String entry) {
list.addElement(entry);
}
public static void RemoveEntry(DefaultListModel list, int entry) {
list.removeElementAt(entry);
}
public static DefaultListModel StrToList(String input, String delimiter) {
DefaultListModel dlmtemp = new DefaultListModel();
input = input.trim();
delimiter = delimiter.trim();
while (input.toLowerCase().contains(delimiter.toLowerCase())) {
int index = input.toLowerCase().indexOf(delimiter.toLowerCase());
dlmtemp.addElement(input.substring(0, index).trim());
input = input.substring(index + delimiter.length(), input.length()).trim();
}
return dlmtemp;
}
public static String ListToStr(DefaultListModel list, String delimiter) {
String result = "";
for (int i = 0; i < list.size(); i++) {
result = list.getElementAt(i).toString() + delimiter;
}
result = result.trim();
return result;
}
public static String LoadFile(String inputfile) throws IOException {
int len;
char[] chr = new char[4096];
final StringBuffer buffer = new StringBuffer();
final FileReader reader = new FileReader(new File(inputfile));
try {
while ((len = reader.read(chr)) > 0) {
buffer.append(chr, 0, len);
}
} finally {
reader.close();
}
return buffer.toString();
}
public static void SaveFile(String outputfile, String outputstring) {
try {
FileWriter f0 = new FileWriter(new File(outputfile));
f0.write(outputstring);
f0.flush();
f0.close();
} catch (IOException ex) {
Logger.getLogger(StringList.class.getName()).log(Level.SEVERE, null, ex);
}
}
}
该方法用于创建具有动态长度的数组
多维数组也可以用这种方法创建。如果有一种描述某些代码的方法,比如。。。。我不知道,给我们看代码…注意,这应该是“ArrayList”,而不是“List”;这给我带来了一些问题。使用List
是正确的。为了讨论原因,Joshua Bloch在中介绍了接口的使用。当我尝试使用JDK 1.6和1.7时,它会导致编译错误。我相信菱形运算符直到1.7才引入。对于1.6,还要指定ArrayList构造函数的类型(newArrayList()
)。作为有效类中方法的主体使用,代码段将按原样在1.7中编译。@EM Creations您是导入java.util.List还是java.awt.List?前一种选择对我有效。
package YOUR_PACKAGE_GOES_HERE;
//This is the StringList Class by i2programmer
//You may delete these comments
//This code is offered freely at no requirements
//You may alter the code as you wish
import java.io.File;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.swing.DefaultListModel;
public class StringList {
public static String OutputAsString(DefaultListModel list, int entry) {
return GetEntry(list, entry);
}
public static Object OutputAsObject(DefaultListModel list, int entry) {
return GetEntry(list, entry);
}
public static int OutputAsInteger(DefaultListModel list, int entry) {
return Integer.parseInt(list.getElementAt(entry).toString());
}
public static double OutputAsDouble(DefaultListModel list, int entry) {
return Double.parseDouble(list.getElementAt(entry).toString());
}
public static byte OutputAsByte(DefaultListModel list, int entry) {
return Byte.parseByte(list.getElementAt(entry).toString());
}
public static char OutputAsCharacter(DefaultListModel list, int entry) {
return list.getElementAt(entry).toString().charAt(0);
}
public static String GetEntry(DefaultListModel list, int entry) {
String result = "";
result = list.getElementAt(entry).toString();
return result;
}
public static void AddEntry(DefaultListModel list, String entry) {
list.addElement(entry);
}
public static void RemoveEntry(DefaultListModel list, int entry) {
list.removeElementAt(entry);
}
public static DefaultListModel StrToList(String input, String delimiter) {
DefaultListModel dlmtemp = new DefaultListModel();
input = input.trim();
delimiter = delimiter.trim();
while (input.toLowerCase().contains(delimiter.toLowerCase())) {
int index = input.toLowerCase().indexOf(delimiter.toLowerCase());
dlmtemp.addElement(input.substring(0, index).trim());
input = input.substring(index + delimiter.length(), input.length()).trim();
}
return dlmtemp;
}
public static String ListToStr(DefaultListModel list, String delimiter) {
String result = "";
for (int i = 0; i < list.size(); i++) {
result = list.getElementAt(i).toString() + delimiter;
}
result = result.trim();
return result;
}
public static String LoadFile(String inputfile) throws IOException {
int len;
char[] chr = new char[4096];
final StringBuffer buffer = new StringBuffer();
final FileReader reader = new FileReader(new File(inputfile));
try {
while ((len = reader.read(chr)) > 0) {
buffer.append(chr, 0, len);
}
} finally {
reader.close();
}
return buffer.toString();
}
public static void SaveFile(String outputfile, String outputstring) {
try {
FileWriter f0 = new FileWriter(new File(outputfile));
f0.write(outputstring);
f0.flush();
f0.close();
} catch (IOException ex) {
Logger.getLogger(StringList.class.getName()).log(Level.SEVERE, null, ex);
}
}
}
DefaultListModel list = new DefaultListModel();
//now that you have a list, you can run it through the above class methods.