Which is a valid declarations of a String?
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String s1 = null;
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String s2 = 'null';
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String s3 = (String) 'abc';
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String s4 = (String) '\ufeed';
To solve this question, the user needs to understand the syntax and rules for declaring a String in Java.
Let's go through each option and explain why it is right or wrong:
A. String s1 = null; This option is a valid declaration of a String. In Java, a String variable can be assigned a null value, which means it does not reference any object. This option is correct.
B. String s2 = 'null'; This option is incorrect. In Java, single quotes (' ') are used to represent characters, not Strings. To declare a String, double quotes (" ") should be used. Therefore, this option is wrong.
C. String s3 = (String) 'abc'; This option is incorrect. In Java, to declare a String, the value must be enclosed in double quotes (" "). The syntax (String) is used for type casting, which is not necessary when declaring a String. Therefore, this option is wrong.
D. String s4 = (String) '\ufeed'; This option is incorrect. The value '\ufeed' is an escape sequence representing a Unicode character. However, to declare a String, the value must be enclosed in double quotes (" "). Therefore, this option is wrong.
The Answer is: A. String s1 = null;
In Java, String s1 = null; is a valid declaration — null is a valid literal for any reference type, including String. String s2 = 'null'; fails because single quotes denote a char literal in Java, not a String, and 'null' has more than one character so it isn't even a valid char. String s3 = (String) 'abc'; fails for the same reason plus you can't cast a char-literal-like construct to String. String s4 = (String) 'ﻭ'; is casting a char (unicode escape) to String, which is also illegal — char cannot be cast to String. Only s1 compiles.