Java中的子字符串搜索

Question

I have a problem with string comparison. For example, there is this string:

"hello world i am from heaven"

I want to search if this string contains "world". I used following functions but they have some problems. I used String.indexof() but if I will try to search for "w" it will say it exists.

In short I think I am looking for exact comparison. Is there any good function in Java?

Also is there any function in Java that can calculate log base 2?

Answer 1

I'm assuming the problems you're having with indexOf() related to you using the character version (otherwise why would you be searching for w when looking for world?). If so, indexOf() can take a string argument to search for:

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

as for log base 2, that's easy:

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

Answer 2

For an exact String comparison, you can simply do:

boolean match = stringA.equals(stringB);

If you want to check that a string contains a substring, you can do:

boolean contains = string.contains(substring);

For more String methods, see the javadocs

Answer 3

You can use

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

This is a simple and easy-to-use function and for a one-liner:

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

Answer 4

Hi My version is as below:

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);

        }
    }
}

Please let me know if it was useful.

Answer 5

I got the solution finally.

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);

                }


            });
    }

Replace the above code with this one:

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 6

Assume you have a below string:

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

Use below code for String to String comparison:

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

Use either of below code to check if your string contains a substring:

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