Java中的字符串子字符串搜索

Question

我对字符串比较有问题。例如，有以下字符串：

"hello world i am from heaven"

我想搜索这个字符串是否包含“world”。我使用了以下函数，但它们有一些问题。我使用了String.indexof()，但如果我尝试搜索“w”，它会说它存在

简而言之，我想我在寻找精确的比较。Java有什么好功能吗

Java中是否有任何函数可以计算log base 2

Answer 1

我终于找到了解决办法

public void onTextChanged(CharSequence s, int start, int before, int count) {

                        ArrayList<HashMap<String, String>> arrayTemplist = new ArrayList<HashMap<String, String>>();
                        String searchString = mEditText.getText().toString();
                        if(searchString.equals("")){new DownloadJSON().execute();}

                    else{


                    for (int i = 0; i < arraylist.size(); i++) {
                        String currentString = arraylist.get(i).get(MainActivity.COUNTRY);
                        if (searchString.toLowerCase().contains(currentString.toLowerCase())) {
    //pass the character-sequence instead of currentstring

                            arrayTemplist.add(arraylist.get(i));
                        }
                    }
                        }
                        adapter = new ListViewAdapter(MainActivity.this, arrayTemplist);
                        listview.setAdapter(adapter);

                }


            });
    }

将上述代码替换为以下代码：

public void onTextChanged(CharSequence s, int start, int before, int count) {

                        ArrayList<HashMap<String, String>> arrayTemplist = new ArrayList<HashMap<String, String>>();
                        String searchString = mEditText.getText().toString();
                        if(searchString.equals("")){new DownloadJSON().execute();}

                    else{


                    for (int i = 0; i < arraylist.size(); i++) {
                        String currentString = arraylist.get(i).get(MainActivity.COUNTRY);
                        if (currentString.toLowerCase().contains(searchString.toLowerCase())) {
    //pass the character-sequence instead of currentstring

                            arrayTemplist.add(arraylist.get(i));
                        }
                    }
                        }
                        adapter = new ListViewAdapter(MainActivity.this, arrayTemplist);
                        listview.setAdapter(adapter);

                }


            });

Answer 2

要进行精确的字符串比较，只需执行以下操作：

boolean match = stringA.equals(stringB);

如果要检查字符串是否包含子字符串，可以执行以下操作：

boolean contains = string.contains(substring);

有关更多字符串方法，请参见javadocs

Answer 3

你可以用

String s = "hello world i am from heaven";
if (s.contains("world")) {
// This string contains "world"
}

这是一个简单易用的函数，适用于单行程序：

String s = "hello world i am from heaven";
if (s.contains("world")) System.out.prinln("It exists!!!!!!!");

Answer 4

嗨，我的版本如下：

package com.example.basic;

public class FindSubString {


    public String findTheSubString(String searchString, String inputString){


        StringBuilder builder = new StringBuilder(inputString);

        System.out.println("The capacity of the String " + builder.capacity());

        System.out.println("pos of" + builder.indexOf(searchString));

        return builder.substring(builder.indexOf(searchString),builder.indexOf(searchString)+searchString.length());
    }

    public static void main(String[] args) {

        String myString = "Please find if I am in this String and will I be found";
        String searchString = "I am in this String";

        FindSubString subString = new FindSubString();

        boolean isPresent = myString.contains(searchString);

        if(isPresent){

        System.out.println("The substring is present " + isPresent + myString.length());

        System.out.println(subString.findTheSubString(searchString,myString));
        }
        else 
        {
            System.out.println("The substring is ! present " + isPresent);

        }
    }
}

请告诉我它是否有用

Answer 5

假设您有以下字符串：

String sampleS = "hello world i am from heaven";

使用以下代码进行字符串到字符串的比较：

boolean is_Equal = sampleS.equals("<any string you want to compare>");

使用以下任一代码检查字符串是否包含子字符串：

boolean is_Contains = sampleS.contains("world");
// OR
boolean is_Contains = (sampleS.indexOf("world") != -1);

Answer 6

我假设你在indexOf()中遇到的问题与你使用字符版本有关（否则，你为什么要在寻找世界时搜索w？）。如果是这样，indexOf()可以使用字符串参数来搜索：

String s = "hello world i am from heaven";
if (s.indexOf("world") != -1) {
  // it contains world
}

至于log base 2，这很简单：

public static double log2(double d) {
  return Math.log(d) / Math.log(2.0d);
}