Question

From Java Language Specification, Chapter 14, Blocks and Statements:

The sequence of execution of a program is controlled by statements, which are
executed for their effect and do not have values.

Some statements contain other statements as part of their structure; such other
statements are substatements of the statement. We say that statement S immediately
contains statement U if there is no statement T different from S and U such that
S contains T and T contains U. In the same manner, some statements contain
expressions as part of their structure.

What does it mean that statement S immediately contains statement U if there is no statement T different from S and U such that S contains T and T contains U.?

Answer 1

Some statements contain other statements as part of their structure; such other
statements are substatements of the statement.

JLS #14.5 defines a statement as:

Statement:

• StatementWithoutTrailingSubstatement
• LabeledStatement
• IfThenStatement
• IfThenElseStatement
• WhileStatement
• ForStatement

So the only statements that can have substatement (= can contain other statements) are labels, if, else, while and for.

The meaning then becomes clearer – if for example, S, T and U are defined as:

if(a == b) //S
    if(c == d) //T
        doSomething(); //U

Statement S immediately contains statement T which immediately contains statement U. But S does not immediately contain U.