JDK10新特性之本地变量类型var的深入理解

int maxWeight = blocks.stream().filter(b -> b.getColor() == BLUE).mapToInt(Block::getWeight)
.max();

ExecutorService executorService= Executors.newSingleThreadExecutor();
Runnable runnable=new Runnable() {
 @Override
 public void run() {
  log.info("inside runnable");
  }
 };
 executorService.submit(runnable);

var executorService= Executors.newSingleThreadExecutor();
var runnable=new Runnable() {
 @Override
 public void run() {
   log.info("inside runnable");
  }
 };
executorService.submit(runnable);

ItIsAVeryLongNameJavaClass itIsAVeryLongNameJavaClass= new ItIsAVeryLongNameJavaClass();

var itIsAVeryLongNameJavaClass= new ItIsAVeryLongNameJavaClass();

var a; //Invalid Declaration - - Cannot use 'var' on variable without initializer
var a = 100; //Valid Declaration

for ( var element : elementList){
  //do something for element
}

for ( var i = 0 ; i < elementList.size(); i++ ){
  System.out.println( elementList.get(i) );
}

public class VarIncorrectUsage {
   
  //var user;  //Not allowed as class fields
     
  //public VarIncorrectUsage(var param){  //Not allowed as parameter 
  //}
 
  /*try{
     
  } catch(var exception){  //Not allowed as catch formal 
 
  }*/
 
  /*public var returnMethod(){ //Not allowed in method return type
    return null;
  }*/
 
  /*public Integer parameterMethod( var input ){ //Not allowed in method parameters
    return null;
  }*/
}

var ints = {1, 2, 3};
var lambda = a -> a;
var methodReference = String::concat;

var var = 2;  //Valid Declaration
     
int var = 2;  //Also valid Declaration