如何在 Java 9 中调试 JShell?
JShell 是一个 REPL 工具,允许运行代码片段,而无需将它们放入类中。该工具提供了一种在 Java 中评估声明、语句和表达式的方法,并且无需创建 main()方法来测试代码的某些部分。
命令 "/debug" 可用于显示 JShell 工具实现的调试信息。一旦输入 "/debug" 命令,调试模式即开启。启用调试模式后,键入简单加法或简单字符串之类的内容,然后按如下所示打印出来。
示例 1
jshell> /debug | Debugging on jshell> 5+3 Compiling: 5+3 Kind: EXPRESSION_STATEMENT -- 5 + 3; compileAndLoad [Unit($1)] ++setCompilationInfo() Snippet:VariableKey($1)#11-5+3 package REPL; import java.io.*;import java.math.*;import java.net.*;import java.nio.file.*;import java.util.*; import java.util.concurrent.*;import java.util.function.*;import java.util.prefs.*; import java.util.regex.*;import java.util.stream.*;class $JShell $11 { public static int $1; public static Object do_it$() throws Throwable { return $1 = 5+3; } } -- diags: [] setStatus() Snippet:VariableKey($1)#11-5+3 - status: VALID compileAndLoad ins = [Unit($1)] -- legit = [Unit($1)] Compiler generating class REPL.$JShell$11 compileAndLoad [Unit($1)] -- deps: [] success: true recordCompilation: Snippet:VariableKey($1)#11-5+3 -- status VALID, unresolved [] $1 ==> 8
示例 2
jshell> /debug | Debugging on jshell> String s = "Adithya" Compiling: String s = "Adithya"; Kind: VARIABLE -- String s = "Adithya" compileAndLoad [Unit(s)] ++setCompilationInfo() Snippet:VariableKey(s)#12-String s = "Adithya"; package REPL; import java.io.*;import java.math.*;import java.net.*;import java.nio.file.*;import java.util.*; import java.util.concurrent.*;import java.util.function.*;import java.util.prefs.*; import java.util.regex.*;import java.util.stream.*;import static REPL.$JShell$11.$1; class $JShell$12 { public static String s; public static Object do_it$() throws Throwable { String s_ = "Adithya"; return s = s_; } } -- diags: [] setStatus() Snippet:VariableKey(s)#12-String s = "Adithya"; - status: VALID compileAndLoad ins = [Unit(s)] -- legit = [Unit(s)] Compiler generating class REPL.$JShell$12 compileAndLoad [Unit(s)] -- deps: [] success: true recordCompilation: Snippet:VariableKey(s)#12-String s = "Adithya"; -- status VALID, unresolved [] s ==> "Adithya"
如果我们想“关闭”调试模式,则再次为同一个会话输入"/debug" 命令。
jshell> /debug | Debugging off
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