Java有惰性求值吗？

我知道 Java 在这种情况下有智能/惰性评估：

public boolean isTrue() {
    boolean a = false;
    boolean b = true;
    return b || (a && b); // (a && b) is not evaluated since b is true
}

但是关于：

public boolean isTrue() {
    boolean a = isATrue();
    boolean b = isBTrue();
    return b || a;
}

Is isATrue()打电话即使isBTrue()返回真？

好吧，就语言而言 - 是的，这两个函数都被调用了。

如果您将函数重写为：

public boolean isTrue() {
    return isBTrue() || isATrue();
}

如果第一个函数为 true，那么第二个函数将不会被调用。

但这是短路评估, not 惰性评估。惰性评估案例看起来像这样：

public interface LazyBoolean {
    boolean eval();
}

class CostlyComparison implements LazyBoolean {
  private int a, b;

  public CostlyComparison(int a, int b) { 
    this.a=a; 
    this.b=b; 
  }

  @Override 
  public boolean eval() {
    //lots of probably not-always-necessary computation here
    return a > b;
  }
} 

public LazyBoolean isATrue() {
  return new CostlyComparison(10,30);  //just an example
}

public boolean isTrue() {        // so now we only pay for creation of 2 objects
    LazyBoolean a = isATrue();   // but the computation is not performed; 
    LazyBoolean b = isBTrue();   // instead, it's encapsulated in a LazyBoolean
    return b.eval() || a.eval(); // and will be evaluated on demand;
                                 // this is the definition of lazy eval.
}