Commonly Used String Processing Functions in Java

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String.startsWith()

Used to detect whether a string starts with a specified prefix.

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public class test {
    public static void main(String[] args) {
        String str = "Test string: hello world!";
        boolean flag1 = str.startsWith("Test");
        System.out.println("str starts with 'Test': " + flag1);
        boolean flag2 = str.startsWith("hello");
        System.out.println("str starts with 'hello': " + flag2);
    }
}

The output of the code is as follows:

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str starts with 'Test': true
str starts with 'hello': false

String.endsWith()

Used to detect whether a string ends with a specified suffix.

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public class test {
    public static void main(String[] args) {
        String str = "Test string: hello world!";
        boolean flag1 = str.endsWith("Test");
        System.out.println("str ends with 'Test': " + flag1);
        boolean flag2 = str.endsWith("!");
        System.out.println("str ends with '!': " + flag2);
    }
}

The output of the code is as follows:

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str ends with 'Test': false
str ends with '!': true

String.contains()

Used to detect whether a specified character or string is contained in a string.

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public class test {
    public static void main(String[] args) {
        String str = "Test string: hello world!";
        boolean flag1 = str.contains("test");
        System.out.println("str contains 'test': " + flag1);
        boolean flag2 = str.contains("string");
        System.out.println("str contains 'string': " + flag2);
    }
}

The output of the code is as follows:

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str contains 'test': false
str contains 'string': true

String.split()

Split a string into a list.

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public class test {
    public static void main(String[] args) {
        String a = "A,B,C,D,E,F,G";
        String[] b = a.split(",");
        for (int i = 0; i < b.length; i++) {
            System.out.print(b[i] + " ");
        }
    }
}

The output of the code is as follows:

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A B C D E F G

String.indexOf()

Returns the index of the first occurrence of the specified substring (or character) in a string. Returns -1 if there is no such substring (or character) in the string.

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public class test {
    public static void main(String[] args) {
        String str = "Test string: hello world!";
        System.out.println("str: " + str);
        System.out.println("str.length()=" + str.length());

        Integer index1 = str.indexOf("t");
        System.out.println("indexOf('t'): " + index1);

        Integer index2 = str.indexOf("o");
        System.out.println("indexOf('o'): " + index2);
    }
}

The output of the code is as follows:

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str: Test string: hello world!
str.length()=25
indexOf('t'): 3
indexOf('o'): 17

String.lastIndexOf()

Returns the index of the last occurrence of the specified substring (or character) in this string. Returns -1 if there is no such substring (or character) in the string.

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public class test {
    public static void main(String[] args) {
        String str = "Test string: hello world!";
        System.out.println("str: " + str);
        System.out.println("str.length()=" + str.length());

        Integer index1 = str.lastIndexOf("t");
        System.out.println("lastIndexOf('t'): " + index1);

        Integer index2 = str.lastIndexOf("o");
        System.out.println("lastIndexOf('o'): " + index2);
    }
}

The output of the code is as follows:

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str: Test string: hello world!
str.length()=25
lastIndexOf('t'): 6
lastIndexOf('o'): 20

StringUtils.substring()

Use String substring(String str, int start, int end) to get the substring with index between [start, end).

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public class test {
    public static void main(String[] args) {
        String str = "Test string: hello world!";
        System.out.println("str: " + str);
        System.out.println("str.length()=" + str.length());
        // 截取区间在[0,4)的字符串
        String subStr = StringUtils.substring(str, 0, 4);
        System.out.println("subStr: " + subStr);
    }
}

The output of the code is as follows:

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str: Test string: hello world!
str.length()=25
subStr: Test