java.io.File - strange behaviour

Question

bbb_bbb 2018-12-29

1
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https://ww2.mathworks.cn/matlabcentral/answers/437613-java-io-file-strange-behaviour

评论： John 2019-5-17

filename='F:\__1\2\test files\file.bin';
success=java.io.File(filename).delete;

invoked from the Matlab Command Window - works,

running as a script - gives error:

"Static method or constructor invocations cannot be indexed.

Do not follow the call to the static method or constructor with any additional indexing or dot references.

MATLAB:staticMethodIndex"

Why is this so?

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Answer 1

Yair Altman 2018-12-30

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With most Java methods, you can follow the method invocation parentheses with a dot, thereby chaining methods. For example: myJPanel.getComponent(0).getComponent(1).setVisible(false). However, such method chaining cannot be done with a constructor - it's valid syntax in Java, but Matlab's interpreter is not smart enough. In this case, simply separate the call into two parts:

filename='F:\__1\2\test files\file.bin';
jFile = java.io.File(filename);
success = jFile.delete;

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Yair Altman 2019-5-17

as far as I am aware, the behavior is the same in this regards in both the command window and scripts - in both cases you cannot chain methods to a Java constructor call, only to other methods.

John 2019-5-17

Nope, they are different. I just tested:

>> ls('D:\tmp')

Figure1.JPG

Figure2.JPG

>> filename = 'D:\temp\Figure1.JPG';

>> success=java.io.File(filename).delete

success =

logical

0

Put those exact lines into a script? and get:

>> Untitled7

Error: Functions cannot be indexed using {} or . indexing.

Error in Untitled7 (line 2)

success=java.io.File(filename).delete;

Conclusion: The parser in the command line, is different from the parser, that parses scripts... That's a bit of a surprise to me, but I'm not into the details of Matlab like you are.

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