如何阅读输入文字？ 爪哇

Question

I need to check if a "user" types in the word "if". Let me explain, i have this: String text;

Scanner read = new Scanner(System.in);
System.out.println("type text");
text=read.nextLine();
System.out.println("the text is " +text);

I need to make sure that what is typed in is a the word "if".

Answer 1

You need to use String API's contains() or equals() methods as shown below:

if(text.contains("if ") || text.contains(" if") || text.contains(" if ")) {
    System.out.println(" Text contains if");
}

The above code works even if the word if is at the start or at the end of the input text .

If you are looking for the whole word match, then you need to use equals() as shown below:

if(text.equals("if")) {
    System.out.println(" Text equals if");
}

Answer 2

You need to compare the value of text with the value if using equals() like this:

if(text.equals("if")){
   //Do something
}

Or a better null safe solution would be:

if("if".equals(text)){}

This way if text is null your program won't crash Thanks to @Tancho for the null safe sollution Generally speaking to compare 2 string you need to use equals() Using == you compare 2 objects references not the values

Answer 3

If you're looking for an exact match, you should use :

"if".equals(text)

Not the other way around, because a constant should always be compared to a variable, not the other way around. You will have : 1. readability 2. safety (as this will never throw a NullPointerException, even if text is null)