Section 2.9 Details of StringsJAVA HAS A BUILT-IN TYPE, String, to represent strings of characters. This type differs from the eight primitive types because a value of type String is an object. A String is not just a data value; it also has "methods." (A method is a subroutine that is part of an object.) For example, if str is a variable of type String, you can call the method str.length(), which is a function that returns the number of characters in the string. There's a lot more you can do with strings. This section covers some of the details. Show
One thing that you cannot do with strings is to use the relational operators <, >, <=, and <= to compare them. You can legally use == and != to compare Strings, but because of peculiarities in the way objects behave, they won't give the results you want. (The == operator checks whether two objects are stored in the same memory location, rather than whether they contain the same value. Occasionally, for some objects, you do want to make such a check -- but rarely for strings. I'll get back to this in a later chapter.) Instead, you should use the methods equals() and equalsIgnoreCase(), which are described below, to compare two Strings. The String class defines a lot of methods. Here are some that you might find useful. Assume that s1 and s2 are Strings:
For the methods s1.toUpperCase(), s1.toLowerCase() and s1.trim(), note that the value of s1 is not changed. Instead a new string is created and returned as the value of the function. The returned value could be used, for example, in an assignment statement such as "s2 = s1.toLowerCase();". Here is another extremely useful fact about strings that I haven't mentioned so far: You can use the operator + to concatenate two strings. The concatenation of two strings is a new string consisting of all the characters of the first string followed by all the characters of the second string. For example, "Hello" + "World" evaluates to "HelloWorld". (Gotta watch those spaces, of course.) Even more surprising is that you can concatenate values belonging to one of the primitive types onto a String using the + operator. The value of primitive type is converted to a string, just as it would be if you printed it to the standard output. For example, the expression "Number" + 42 evaluates to the string "Number42". And the statements TextIO.put("After "); TextIO.put(years); TextIO.put(" years, the value is "); TextIO.put(principal); can be replaced by the single statement: TextIO.put("After " + years + " years, the value is " + principal); Obviously, this is very convenient. It would have shortened several of the examples used earlier in this chapter. You can even use the += operator to add something onto the end of a String. For example, if you want to read a sequence of letters from standard input and store them in a String, you could do it like this: String str = ""; // start with an empty string char ch = TextIO.getChar(); // read one character while ( (ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z') ) { // ch is a letter, so append it to the string // and read the next character. str += ch; // (note: same as str = str + ch;) ch = TextIO.getChar(); } // end of while loop End of Chapter 2 Which method call gives the position of the first occurrence of x in String s1?indexOf("X")
Which of the following method call gives the position of the first occurrence of x in the String s1 A s1 indexOf x B s1 indexOf x N C s1 Index x 1 D s1 index x N?The Java String class indexOf() method returns the position of the first occurrence of the specified character or string in a specified string.
What is use of charAt () method Mcq?Explanation: charAt() is a method of class String which gives the character specified by the index.
Which of these method will modify the value of a string s?a) String replace(char original, char replacement): This method replaces one and only character from the original string. For example, String S=”Hello”. replace('e', 'x'); gives us Hwllo as the value of S.
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