Why is "while((String tmp=x))" not valid Java syntax?

Question

I have a clarification about some Java code: What's the difference between these codes, that one can be compiled while the other cannot. I'm not interested on "how to fix the error" because I've already solved it, but more on an explanation about the problem: Working ``` public void x(){ HashMap count= new HashMap(); Scanner scan= new Scanner("hdsh"); String tmp; while((tmp=scan.next())!=null){ if(count.containsKey(tmp)){ count.put(tmp, 1); } else{ count.put(tmp, count.get(tmp)+1); } tmp=scan.next(); } } ``` Not Working ``` public void x(){ HashMap count= new HashMap(); Scanner scan= new Scanner("hdsh"); while((String tmp=scan.next())!=null){ if(count.containsKey(tmp)){ count.put(tmp, 1); } else{ count.put(tmp, count.get(tmp)+1); } tmp=scan.next(); } } ``` The errors of Eclipse are: Multiple markers at this line: - String cannot be resolved to a variable - Syntax error on token "tmp", delete this token - String cann…

Accepted Answer

JLS §14.12:

```
WhileStatement:
    while ( Expression ) Statement
```

JLS §15.27

```
Expression:
    AssignmentExpression
```

JLS §15.26

```
AssignmentExpression:
    ConditionalExpression
    Assignment

Assignment:
    LeftHandSide AssignmentOperator AssignmentExpression

LeftHandSide:
    ExpressionName
    FieldAccess
    ArrayAccess
```

`LeftHandSide` cannot be a declaration, so it is not allowed.

Why is "while((String tmp=x))" not valid Java syntax?

Solution

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